The Doctor walked into his physics laboratory with a certain Jemma Simmons behind him, smiling at the kids. "Good morning, class! Are we sitting comfortably?" He grinned, beginning to write on the board. "So. Physics! Physics, eh? Physics. Physics. Physics! Physics. Physics, physics, physics, physics, physics, physics, physics!" He looked over his shoulder. "I hope one of you is getting all this down. OK! Let's see what you know!" He put down the chalk. "Two identical strips of nylon are charged with static electricity and hung from a string so they can swing freely. What would happen if they were brought near each other?" He looked at a young boy with spectacles, whose hand was in the air. "Yes! Er, what's your name?"

"Milo."

"Milo!" He grinned at the name. "Off you go, then!"

"They'd repel each other because they have the same charge."

The Doctor brightened. "Correctamundo!" He grimaced. "A word I have never used before, and hopefully never will again." Jemma coughed from where she sat at another desk, and he winked at her before beginning to pace. "Question two, Miss Simmons?"

"Yes, sir," she agreed, standing up. "So, I coil up a thin piece of microwire and place it in a glass of water. Then I turn on the electricity and measure to see if the water's temperature is affected. Here's the question: how do I measure the electrical power going into the coil?" The Doctor was surprised when only Milo's hand went up. Jemma looked around, surprised as well. "Someone else?" No one answered. "No? OK, then. Milo. Go for it."

"Measure the current and PDs in an ammeter and a voltmeter."

Jemma blinked. "Two for Milo."

The Doctor leaned forward. "Milo, tell me this. True or false. The greater the dampening of the system, the quicker it loses energy to its surroundings?"

"False," he replied instantly.

"What is non-coding DNA?" Jemma asked immediately afterwards.

"DNA that doesn't code for a protein," he shot back barely a second later.

"Sixty five thousand nine hundred and eighty three times five?"

"Three hundred and twenty nine thousand nine hundred and fifteen."

"How do you travel faster than light?" the Doctor asked. He can't get this.

"By opening a quantum tunnel with an FTL factor of thirty six point seven recurring."

The Doctor's jaw dropped, and he looked at Jemma in shock. "Told you," she mouthed.

***

After a few more classes, the Doctor and Jemma slid down the lunch line. The Doctor looked up when someone slapped mash onto his tray, and he met a pair of angry dark eyes. He looked over her shoulder to meet an equally dark pair of eyes. The Doctor and Jemma looked at each other and begin to snicker, walking away towards one of the empty tables. "We're so dead later," Jemma laughed.

"Worth it," the Doctor told her.

A few minutes later, a cloth dropped onto the table, and Jessie began scrubbing. "Two days," she grumbled.

"Sorry, could you just - " The Doctor pointed to a spot on the table, grinning. "There's a bit of gravy." Jessie glared at him and scrubbed harder. "No, no. Just . . . just there."

Jemma giggled, and Jessie growled. "Two days we've been here."

"Blame Saleen," the Doctor told her. "She's the one who put us into this. And she was right. Boy in class this morning, got a knowledge way beyond Earth."

"You eating those chips?" Jessie asked, pointing.

The Doctor nodded, jabbing one with his fork. "Yeah. They're a bit different."

"Oh, I think they're gorgeous," Jemma sighed, chewing. "Wish I had school dinners like this."

"It's very well behaved, this place," the Doctor said, looking around.

"Mmmhmm," Jessie agreed, rolling her eyes.

"I thought there'd be happy slapping hoodies," he continued, tilting his head. "Happy slapping hoodies with ASBOs. Happy slapping hoodies with ASBOs and ringtones." Jemma snorted into her chips, and Jessie began snickering. "Huh? Huh?" He glared. "Don't tell me I don't fit in!"

One of the other dinner ladies walked over - Jackson, the Doctor remembered - glaring at Jessie. "You are not permitted to leave your station during a sitting," she said.

"I was just talking to these teachers," Jessie replied.

Jemma waved. "Hi."

"Hello," the Doctor put in, waving as well.

"He doesn't like the chips," Jessie stage whispered.

Jemma choked on one of her chips, and the Doctor thumped her on the back. Jackson glared at him. "The menu has been specifically designed by the headmaster to improve concentration and performance. Now get back to work."

Jessie growled. "You see? This is me. And May. Cafeteria ladies."

"I'll have the crumble," Jemma told her.

Jessie groaned. "I'm so going to kill you both."

The Doctor and Jemma just burst out laughing as Jessie returned behind the counters.

***

Melinda May and Jessie began drying the dishes when the double doors swung open. They ducked behind a rack and watched as the cafeteria ladies wheeled a large cooking oil drum in. May's phone rang, and she answered it. "What you got?" she asked.

"Confirmation," Fitz replied. "We've just got into army records. Three months ago, massive UFO activity. They logged over forty sightings. Lights in the sky, all of that."

"We can't get any photos, because then it gets all classified and secret," Saleen added. "Keeps locking us out."

"Tell you what, though," Jessie said. "Three months ago, turns out all the kitchen staff were replaced. And this lot is just weird."

"See?" Saleen crowed. "There's definitely something going on. I was right to call you home."

"I thought maybe you just called me home just . . . well . . . " Jessie blushed. "Just to call me home."

"Do you think we'd just invent an emergency?" Fitz asked.

"You could've done," Jessie pointed out.

"That's the last thing we'd do."

"Watch it!" Jackson barked.

"Because every time we see you," Saleen continued, "an emergency just gets in the way."

One of the oil barrels toppled over, and one lady was splattered. She began screaming, and May quickly hung up as that woman was taken into the office, the blinds being drawn. She quickly began dialing another number when Jackson noticed. "What're you doing?" she demanded.

May held up her phone. "Calling an ambulance."

"No need," Jackson replied. "She's quite all right." Jessie raised an eyebrow when there was the sound of something being ignited, and a scream. Jackson narrowed her eyes. "It's fine. She does that."

"I bet she does," May muttered as Jackson vanished into the office, now filled with smoke.

Jessie didn't pay attention as she looked at the oil just spilled. "And I'm pretty sure that this oil eats through metal."

***

"Thanks, Jemma," the Doctor told Jemma as she handed him a bottle of water.

"Yesterday," Mr. Parsons was saying, "I had a twelve year old girl give me the exact height of the Walls of Troy in cubits."

"And it's ever since the new headmaster arrived?" the Doctor asked casually.

"Finch arrived three months ago," Mr. Parsons confirmed. "Next day, half the staff got flu. Finch replaced them with that lot, except for the teacher you two replaced, and that was just plain weird, her winning the lottery like that."

"How's that weird?" Jemma asked just as casually.

"She never played. Said the ticket was posted through her door at midnight."

"Hmm . . . " The Doctor sent a quick wink to Jemma, who grinned. "The world is very strange."

"Excuse me, colleagues!" The Doctor turned to see Mr. Finch had entered, and he drew in a breath when he saw who he had with him. "A moment of your time. May I introduce Miss Sarah Jane Smith. Miss Smith is a journalist who's writing a profile about me for the Sunday Times. I thought it might be useful for her to get a view from the trenches, so to speak. Don't spare my blushes."

Jemma nudged him. "D'you know her?" she whispered.

"Is it that obvious?" he asked.

"Don't tell Jessie."

"Hello."

The Doctor's head jerked up as Sarah Jane approached them. He couldn't help but smile. "Oh, I should think so."

"And you are?" she asked.

The Doctor blinked when Jemma nudged him harder. "Hm? Er, Smith. John Smith."

"Jemma Simmons," Jemma introduced herself.

"John Smith," Sarah Jane murmured. "I used to have a friend who sometimes went by that name."

"Well, it's a very common name," the Doctor replied.

"He was a very uncommon man." She smiled, holding out a hand. "Nice to meet you."

Jemma shook it, then the Doctor. "Nice to meet you. Yes, very nice. More than nice. Brilliant!"

"Don't scare her away!" Jemma whined.

Sarah Jane blushed a little. "Er, so . . . er, have you worked here long?"

"It's our second day," Jemma replied.

"Oh, so you're new, then!" Sarah Jane said enthusiastically. "So, what do you think of the school? I mean, this new curriculum? So many children getting ill. Doesn't that strike you as odd?"

"You don't sound like someone just doing a profile," Jemma noted.

Sarah Jane smirked a little. "Well, no harm in a little investigation while I'm here."

"No," the Doctor agreed. "Good for you." He continued nodding and grinning even as she walked away. "Good for you. Oh, good for you, Sarah Jane Smith!"

***

"Oh, it's weird seeing school at night," Jessie commented as the six of them entered the school later that night. "It just feels wrong."

"I remember you talking about that," Fitz said.

"Yeah, I used to think all the teachers slept in school."

"All right, team!" the Doctor announced, then made a face. "Oh, I hate people who say team. Er, gang." He made another face. "Er . . . comrades." He shook his head. "Anyway, Jessie, May, go to the kitchen. Get a sample of that oil." He looked at Saleen and Fitz. "Saleen, Fitz, the new staff are all maths teachers. Go and check out the maths department. Jemma and I are going to look in Finch's office. Be back here in ten minutes."

Jessie turned to look at Fitz and Saleen as the Doctor and Jemma left. "You going to be all right?"

"Me?" Fitz scoffed. "Please. Infiltration and investigation? I'm an expert at this." The two of them went down a hallway, and then Fitz came back. "Where's the maths department?"

May raised an eyebrow. "Down there, turn left, through the fire doors, on the right."

"Thank you."

Jessie snickered as he left. "No wonder the Doctor called him Fizz."

May just snorted as they headed for the kitchen.

***

The Doctor and Jemma walked through the corridors when the Doctor held out an arm. "Hold on."

"What?" Jemma whispered, then saw what he had seen. The storage room door that held the TARDIS was open. "Should we - ?"

"Wait a tick."

A second later, Sarah Jane came backing out. "Hello, Sarah Jane," the Doctor said softly.

She spun around, staring at the Doctor wide-eyed. "It's you," she whispered. "Oh, Doctor. Oh, my God, it's you, isn't it?" She slowly walked forward. "You've regenerated."

He gave a small smile. "Yeah. Half a dozen times since we last met."

"That was with the fedora and scarf, right?" Jemma asked, wracking her memory.

The Doctor nodded. "You're good."

"Thank you!"

"You look incredible," Sarah Jane breathed.

"So do you," the Doctor countered.

She shrugged. "Huh. I got old." She looked at Jemma appraisingly. "Are you the new assistant?"

Jemma blinked. "What?"

"No, Jemma here is one of the group that told us what was going on here."

"What are you doing here?"

"Well . . . " The Doctor grinned. "UFO sighting. School gets record results. I couldn't resist. What about you?"

"The same," she laughed, then sobered. "I thought you'd died. I waited for you and you didn't come back, and I thought you must have died."

"I lived. Everyone else died."

"What do you mean?"

"Everyone died, Sarah."

"The Time War," Jemma whispered. "Jessie mentioned that."

The Doctor winced. Sarah Jane noted it. "I can't believe it's you," she said.

Two screams were heard simultaneously from down the hall, and Jemma perked up. "That was Fitz!"

"OK, now I can!" Sarah Jane declared as they began running.

Running came from the opposite direction, and Jessie and May ran up, Jessie holding a sample cup, May wielding a gun. "Did you hear that?" May asked.

Jessie got to the more pressing issue and peered over Jemma's shoulder at Sarah Jane. "Who's she?"

"Jessie, May, Sarah Jane. Sarah Jane, May, Jessie."

"Hi," Sarah Jane said brightly. "Nice to meet you." She turned to the Doctor. "You can tell you're getting older. Your assistants are getting younger."

Jessie bristled. "I'm not his assistant."

"No?" Sarah Jane winked. "Get you, tiger."

***

"Sorry!" Fitz apologized profusely as the five made it to the maths department. "Sorry, it was us. You told us to investigate - "

"We started looking through some of the cupboards, and all of these fell out on us," Saleen finished, folding her arms and observing the mess they'd made.

"Oh my God, they're rats," Jessie whispered, looking around. "Dozens of rats. Vacuum packed rats."

The Doctor raised an eyebrow. "And you decided to scream?"

"It took me by surprise!" Fitz protested.

"I expected Saleen, but you? Like a little girl, too?"

"It was dark, and I was covered in rats!"

Jessie snorted, and the Doctor grinned. "Nine, maybe ten years old. I'm seeing pigtails, frilly skirt."

"Can we focus here?" Jessie asked, snapping her fingers in front of his nose, making him jerk back. "Anyone else see something strange about this? Rats in school?"

"Well, obviously they use them in biology lessons," Sarah Jane replied, and Jessie raised an eyebrow. "They dissect them. Or maybe you haven't reached that bit yet. How old are you?"

"No one dissects rats in school anymore," Jemma quickly jumped in before Jessie could say something insulting. "They haven't done that for years."

"Where are you from, the Dark Ages?" Jessie quipped.

"Anyway," the Doctor said loudly as Sarah Jane began to open her mouth. "Moving on. Everything started when Mr. Finch arrived. We should go and check his office."

"This way," May said, pointing and leading the way.

Jessie ran to catch up to Sarah Jane. "I don't mean to be rude or anything, but, who exactly are you?"

"Sarah Jane Smith," she replied. "I used to travel with the Doctor."

"Hmm." She looked at him over her shoulder. "Which one?"

Sarah Jane blinked. "Two of them."

"Description? Celery on the lapel? Pocket watch? Question marks?" Jessie pressed.

"If you must know, it was first one had an opera cape, and then a fedora and a long scarf."

"Three and Four. Huh. Well. He's never mentioned you."

"Oh, I must've done!" the Doctor said from behind them, FitzSimmons and Saleen flanking him. "Sarah Jane. Mention her all the time."

"Hold on." Jessie pretended to think, then shook her head. "Sorry. Never."

She ran to catch up with May. "What?" Sarah Jane asked in surprise. "Not even once? He didn't mention me even once?"

"And may the Deathbringer of Asgard be unleashed," Saleen joked.

"Ho ho, mate!" Fitz crowed. "The missus an the ex. Welcome to every man's worst nightmare."

***

The Doctor sonicked the lock on Finch's office and opened it. He took one look at the ceiling and looked back. "Jess, you know how you used to think all the teachers slept in the school? Well . . . " He held the door open further. "They do."

Jessie gagged when she saw what appeared to be giant bats hanging from the ceiling. "No way!" Saleen gasped in surprise.

She and FitzSimmons simultaneously turned tail and began to run. The rest of them followed suit. "I am not going back in there," Fitz stated. "No way."

"Those were teachers," Jessie whispered.

"When Finch arrived, he brought with him seven new teachers, four dinner ladies, and a nurse."

"Thirteen," May agreed. "There were thirteen bat people in there."

"Come on," the Doctor said, turning to go back into the school.

"Come on?" Fitz echoed. "You've got to be kidding!"

"I need the TARDIS," the Doctor explained. "I've got to analyze that oil from the kitchen."

Sarah Jane tugged on his arm. "I might be able to help you there. I've got something to show you."

Jessie looked as Sarah Jane unlocked the back end of her car. When she opened it, the Doctor brightened considerably. "K9!" he cried gleefully, and Jessie raised an eyebrow at the metal dog. "Jessie Nightshade, Saleen Harper, Melinda May, Leo Fitz, Jemma Simmons, allow me to introduce K9! Well, K9 Mark III to be precise."

"Why does he look so disco?" Jessie asked.

"Oi!" the Doctor protested. "Listen, in the year five thousand, this was cutting edge." He looked K9 over. "What's happened to him?"

"Oh, one day, he just . . . nothing," Sarah Jane answered.

"Well, didn't you try and get him prepared?"

Everyone simultaneously turned to him, jaws dropping. "Well, it's not like getting parts from a Mini Vetro," Sarah Jane retorted. "Besides, the technology inside him could rewrite human science. I couldn't show him to anyone."

"I think he's cute," Jemma commented.

"Good taste, Agent Simmons," the Doctor praised.

"Agent?" Sarah Jane squeaked. "You work with agents?"

"Strategic Homeland Intervention, Enforcement, and Logistics Division," May replied, and five SHIELD badges were flashed at Sarah Jane. "SHIELD for short."

"Ooh, what's the nasty lady down to you, eh?" the Doctor asked in a baby voice.

Jessie stared at him in shock. "Look, no offense, but could you two just stop petting for a minute? Never mind the tin dog. We're busy!"

***

"You see," Saleen said as Jessie waited for their chips to be done, FitzSimmons working with the Doctor and Sarah Jane on K9. "What's impressive is that it's been nearly an hour since we met her and I still haven't said 'I told you so.'"

Jessie growled. "I'm not listening to this."

"Although, I have prepared a little 'I was right' dance that I can show you later." Jessie handed the proper money over to the server and took her basket. "All this time you've been giving it. He's different, when the truth is he's just like any other guy."

"You don't know what you're talking about."

"Maybe. But if I were you, I'd go easy on the chips."

***

"God, this is fascinating," Fitz gushed as he looked at the inside of K9. "Bloody hell . . . "

The Doctor grinned. "Rocket science doesn't beat technology from the future, eh?"

"No way," Jemma agreed, holding a flashlight up.

"You know," Sarah Jane began, "I thought of you on Christmas Day. This Christmas just gone? Great big spaceship overhead. I thought, 'oh yeah, bet he's up there.'"

"Right on top of it, yeah," the Doctor agreed, fiddling with his sonic screwdriver.

"And Jessie?"

The Doctor nodded. "She was there, too, along with Saleen and May."

"Did I do something wrong?" Sarah Jane asked timidly. "Because you never came back for me. You just . . . dumped me."

"I told you, I was called back home, and in those days, humans weren't allowed."

"And now it's gone, right?" Jemma asked.

The Doctor swallowed. "Yeah."

"I waited for you," Sarah Jane told him. "I missed you."

"Oh, you didn't need me! You were getting on with your life."

"You were my life." FitzSimmons looked between Sarah Jane and the Doctor. "You know what the most difficult thing was? Coping with what happens next, or with what doesn't happen next. You tok me to the furthest reaches of the galaxy. You showed me supernovas, intergalactic battles, and then you just drop me back on Earth."

"There was the Chitauri invasion," Fitz offered. "And the Dark Elf conundrum."

"Conundrum," the Doctor tried out. "I kind of like that. Thanks, Fizzy boy."

"Fitz," he muttered, and Jemma giggled.

"How could anything compare to that?" Sarah Jane asked.

"You could apply for SHIELD," Jemma offered.

"All those things you saw," the Doctor said, turning to Sarah Jane. "Do you want me to apologize for that?"

"No," Sarah Jane replied quickly. "But we get a taste of that splendor, and then we have to go back."

"Look at you, you're investigating! You found that school. You're doing what we always did."

"You could've come back."

"I couldn't."

"Why not?"

The Doctor didn't answer. Jemma looked over her shoulder to see Jessie, Saleen, and May eating. She turned back to the Doctor. "Doctor?" she asked hesitantly.

He didn't answer her either. "It wasn't Croydon, where you dropped me off," Sarah Jane told the Doctor. "That wasn't Croydon."

"Where was it?" he asked, still working on K9.

"Aberdeen."

Fitz snorted loudly. "Right," the Doctor said absently, then looked back at her. "That's next to Croydon, isn't it?" Jemma laughed, and then K9's lights came on. "Oh, hey!" the Doctor cheered. "Now we're in business!"

"Master," K9 said in a robotic voice.

"He recognizes me!"

"Affirmative."

"Jess, give us the oil."

Jessie slipped it out of her pocket and handed it to him. "I wouldn't touch it, though. That dinner lady got all scorched."

"I'm no dinner lady," the Doctor assured her with a smirk. "And I don't often say that." He smeared the oil onto K9's probe, and he watched as K9 began scanning. "Here we go. Come on, boy. Here we go!"

"Ex-ex-extract," K9 stuttered. "Ana-ana-analyzing."

"Listen to him, man," Saleen said in surprise. "That's a voice!"

"Careful," Sarah Jane warned. "That's my dog!"

"Confirmation of analysis," K9 reported. "Substance is Krillitane Oil."

The Doctor sucked in a breath. "They're Krillitanes."

"Is that bad?" May asked.

"Very," the Doctor agreed. "Think of how bad things could possibly be, and add another suitcase full of bad."

"And what are Krillitanes?" Sarah Jane asked.

"They're a composite race," the Doctor began to explain. "Just like your culture is a mixture of traditions from all sorts of countries, people you've invaded or have been invaded by. You've got bits of Viking, bits of France, bits of whatever. The Krillitanes are the same. An amalgam of the races they've conquered. But they take physical aspects as well. They cherry pick the best bits from the people they destroy. That's why I didn't recognize them. The last time I saw Krillitanes, they looked just like us except they had really long necks."

"What're they doing here?" Jemma asked.

The Doctor's eyes widened in realization. "It's the children. They're doing something to the children."

***

"So what's the deal with the tin dog?" Saleen asked as she and May helped put K9 back in the trunk of Sarah's car.

"The Doctor likes traveling with an entourage," Sarah Jane explained. "Sometimes they're humans, sometimes they're aliens, and sometimes they're tin dogs. What about you? Where do you fit in the picture?"

"FitzSimmons and I are part of a SHIELD team that investigates anything supernatural here," May replied. "I'm the pilot."

"And me?" Saleen asked. "I'm sort of the go-between girl. I'm kind of the technical support. I'm - " She cut off, eyes widening. "Oh my God. I'm the tin dog."

***

"How many of us have there been traveling with you?"

The Doctor turned to look at Jessie as she followed him out. "Does it matter?" he asked, trying to avoid the topic.

"Yeah, it does, if I'm just the latest in a long line," Jessie replied.

"As opposed to what?"

"I knew you were other people before this, but I thought you and me . . . I thought it was just the two of us." She shook her head. "I obviously got it wrong. I've been to the year five billion, right? But this . . . " She nodded to Sarah Jane, who was talking to Saleen and May. "Now this is really seeing the future. You just leave us behind. Is that what you're going to do to me?"

And truthfully, the Doctor's hearts clenched at her accusation. "No," he replied instantly. "Not to you."

"But Sarah Jane?" she pressed. "You were that close to her once, and now you never even mention her. Why not?"

"You know what happens to me," he tried to explain. "I don't age. I regenerate. Humans decay. You wither and you die. Imagine watching that happen to someone who you - " He cut off abruptly, not letting the one word he wanted to say slip out.

Jessie raised an eyebrow. "What, Doctor?"

He tried to say it a different way. "You can spend the rest of your life with me, but i can't spend the rest of mine with you. I have to live on. Alone. That's the curse of the Time Lords."

There was a screech, and the Doctor looked up as one of the Krillitanes swooped down. He grabbed Jessie by the shoulders and pulled her down with him as it swooped around them, almost hitting Sarah Jane. "Was that a Krillitane?" Jemma asked.

"But it didn't even touch her!" May said. "It just flew off! What did it do that for?"

***

The Doctor watched the students enter the school the next morning, crossing his arms. "Jess and Sarah, you go to the maths room. Crack open those computers. I need to see the hardware inside." He took his sonic screwdriver out of his pocket. "Here. You might need this." He handed it to Sarah Jane. "Saleen, FitzSimmons, surveillance. I want you outside. I need eyes on everything."

"Just stand outside?" Saleen asked incredulously.

"Here," Sarah Jane said, fishing her car keys out. "Take these. You can keep K9 company."

She tossed the keys into the air, and Fitz caught them. "Don't forget to leave the window open a crack," the Doctor added.

"But he's metal!" Fitz protested.

The Doctor grinned. "I didn't mean for him."

"What're you going to do?" Jessie asked.

The Doctor turned to May with a smile. "Melinda May, I think it's time I had a word with Mr. Finch. Care to join me?"

***

The students ran past them on the staircase as the Doctor and May walked down one set. The Doctor looked over the railing once to see Finch observing the students. The man stiffened and looked up, meeting the eyes of the Doctor before heading for the swimming pool. "Keep an eye on him, will you?" the Doctor asked May as they headed in that direction as well.

"You got it," she replied, hand going for the gun on her side.

They entered on one end of the pool to see Finch standing on the other side. "Who are you?" the Doctor asked.

"My name is Brother Lassa," Finch replied. "And you?"

"The Doctor," the Doctor introduced himself, then nodded to May. "And this is Melinda May. Since when did Krillitanes have wings?"

"It's been our form for nearly ten generations now. Our ancestors invaded Bessan. The people there had some rather lovely wings. They made a million windows in one day. Just imagine."

"And now you're looking human," May said.

"A personal favorite, that's all," Finch replied.

"And the others?" the Doctor asked.

"My brothers remain bat form," Finch answered. "What you see is a simple morphic illusion. Scratch the surface, and the true Krillitane lies beneath." He tilted his head. "And what of the Time Lords? I always thought of you as such a pompous race. Ancient, dusty senators so frightened of change and chaos. And of course, they're all but extinct. Only you. The last."

"Ignore him," May whispered in his ear.

The Doctor nodded microscopically. "This plan of yours. What is it?"

"You don't know," Finch said, sounding surprised.

"That tends to be why people ask," May retorted.

"Well, show me how clever you are," Finch told the Doctor, holding his hands out. "Work it out."

"If I don't like it, then it will stop," the Doctor warned.

"Fascinating." Finch walked closer. "Your people were peaceful to the point of indolence. You seem to be something new. Would you declare war on us, Doctor?"

"I would," May muttered.

"I'm so old now," the Doctor replied. "I used to have so much mercy. You get one warning. That was it."

"But we're not even enemies," Finch said softly. "Soon you will embrace us." He looked both of them over. "The next time we meet, you will join with me. I promise you both."

***

"I'm wondering if I should've gone with Jessie and Sarah Jane," Jemma commented as she looked on her tablet. "Jessie would kill Sarah Jane if she got the chance."

"Still, he could've sent us back to the Bus," Fitz pointed out.

"Surveillance," Saleen snorted. "If you ask me, it's just another way of saying 'go sit at the back of the class with the safety scissors and glitter.'" She looked at K9, then sighed. "That's me talking to a metal dog, then."

***

"It's not working."

Jessie held out her hand for the sonic screwdriver as Sarah Jane smacked it against her palm. "Give it to me."

Sarah Jane handed it over, and Jessie began to work on the wires. "Used to work first time in my day."

"Things were a lot simpler back then."

"Jessie, can I give you a bit of advice?"

Jessie raised an eyebrow at her. "I've got a feeling you're about to anyway."

"I know how intense a relationship with the Doctor can be, and I don't want you to feel like I'm intruding."

Jessie blinked. "I don't feel threatened by you if that's what you mean."

"Right," Sarah Jane said quickly. "Good. Because I'm not interested in picking up where we left off."

"No?" she asked, starting to get a little carried away with no one to stop her. "With the big sad eyes and the robot dog?" She snorted. "What else were you doing last night?"

"I was just saying how hard it was adjusting to life back on Earth!"

"The thing is," Jessie said, going back to the wires. "When you two met, they'd only just got rid of rationing. No wonder all that space stuff was a bit too much for you."

"I had no problem with space stuff!" Sarah Jane cried. "I saw things you wouldn't believe!"

"Oh, this'll be good," Jessie laughed, standing up and folding her arms. "Try me, then."

"Mummies."

"I've met ghosts."

"Robots. Lots of robots."

"Slitheen." She smirked. "In Downing Street."

"Daleks!"

"Met and killed the Emperor," Jessie retorted.

"Anti-matter monsters."

"Gas masked zombies and Chitauri."

"Real living dinosaurs!"

"Real living werewolf!"

"The Loch Ness Monster!"

Jessie blinked. "Seriously?" Sarah Jane bit her lip, and Jessie shook her head. "Listen to us," she chuckled. "It's like me and my other best friend, Skye. The only time we fell out was over a man, and we're arguing over the Doctor." She grinned. "With you, did he do that thing where he'd explain something at, like, ninety miles per hour, and you'd go 'what?' and he'd look at you like you'd just drooled on your shirt?"

Sarah Jane grinned. "All the time. Does he still stroke bits of the TARDIS?"

Jessie began to giggle. "Yeah! Yeah, he does." She laughed louder. "I'm like, 'do you two want to be alone?'"

They shared a laugh and burst out laughing. The Doctor and May entered behind them, not noticing them. "How's it going?" he asked. Jessie and Sarah Jane looked at each other before laughing even harder, practically doubling over. The Doctor frowned and looked at May in confusion. "What?" May shrugged, holding up her hands, and the Doctor turned back to them. "Listen, I need to find out what's programmed inside these."

Jessie began laughing hysterically, doubling over and having to clutch onto a table for support. Sarah Jane wasn't much better. May looked like she was trying to contain a grin, but the Doctor was still utterly confused. "What?" he asked. "Stop it!"

***

"All pupils to class immediately." Jemma looked up from her tablet when the announcement came on the loudspeaker. "And would all members of staff congregate in the staff room."

"That's not right," Fitz said, checking his phone. "Schedule says they shouldn't be going inside for another ten minutes."

"Something's not right, then," Saleen murmured, straightening up. "I just wonder what."

***

"I can't shift it," the Doctor said as he tried to use the sonic screwdriver.

"I thought the sonic screwdriver could open anything!" Sarah Jane exclaimed.

"Anything except a deadlock seal," the Doctor corrected. "There's got to be something inside here. What're they teaching those kids?"

***

The doors to the school slammed shut, and Jemma jumped in her seat. "What the - ?"

"There's still a kid there!" Fitz said, pointing.

Jemma saw the boy shaking the door handles, trying to get them open. "They've taken them all!" he mouthed.

"What?" Saleen asked.

"They've taken all the children!"

***

Sarah Jane pointed to one of the screens. "You wanted the program? There it is."

The Doctor leaned in closer to take a look. "Some sort of code . . . "

***

Jemma began pressing buttons on K9. "Come on," she said. "We need some help!"

Fitz hit K9 on the head, and he powered up. "System restarted," K9 reported. "All primary drives functioning!"

"You're working!" Jemma cheered, then sobered. "OK. No time to explain. We need to get inside the school. Do you have, like . . . I don't know, a lock picking device?"

"We are in a car," K9 observed.

"Maybe a drill attachment?" she tried again.

"We are in a car," K9 repeated.

"Fat lot of good you are," Fitz muttered.

"We are in a car."

Saleen's eyes widened. "Wait a second," she murmured. "We're in a car." She grinned, then gestured to Kenny. "Get back!"

***

The Doctor's eyes widened. "The Skasis Paradigm. They're trying to crack the Skasis Paradigm!"

"The Skasis what?" Sarah Jane asked.

"The God maker," the Doctor explained. "The universal theory. Crack that equation, and you've got control of the building blocks of the universe. Time and space and matter, yours to control."

"What, and the kids are like a giant computer?" May asked.

The Doctor nodded. "Yes, and their learning power is accelerated by the oil. That oil from the kitchens. It works as a . . . as a conducting agent! Makes the kids cleverer."

Jessie's eyes widened. "But that oil's on the chips. I've been eating them."

The Doctor tilted his head. "What's fifty nine times thirty five?"

The numbers popped into her head instantly. "Two thousand and sixty five." Her eyes widened.

"Oh my God," May whispered in shock.

"But why use children?" Sarah Jane asked. "Can't they use adults?"

"No, it's got to be children," the Doctor replied. "The God maker needs imagination to crack it. They're not just using the children's brains to break the code. They're using their souls."

"Let the lesson begin." Both Jessie and May turned immediately, drawing their guns and aiming them at Finch, who had entered behind them. "Think of it, Doctor. With the Paradigm solved, reality becomes clay in our hands. We can shape the universe and improve it."

"Oh yeah?" the Doctor asked with a snort. "The whole of creation with the face of Mr. Finch? Call me old fashioned, but I like things as they are."

"You act like such a radical, and yet all you want to do is preserve the old order? Think of the changes that could be made if this power was used for good."

"What? By someone like you?"

"No. Someone like you." The Doctor faltered, and Jessie took a step closer to him as Finch approached, May keeping her gun trained on him. "The Paradigm gives us power, but you could give us wisdom. Become a God at my side. Imagine what you could do! Think of the civilizations you could save. Perganon. Assinta. Your own people, Doctor, standing tall." Jessie clicked the safety off, and May did the same when Finch mentioned the Time Lords. "The Time Lords reborn."

"Doctor, don't listen to him," Sarah Jane pleaded.

"And you could be with him throughout eternity," Finch added, looking at Sarah Jane. She stopped as well, and May stepped towards her. "Young, fresh, never wither, never age, never die." He smiled at the Doctor. "Their lives are so fleeting. So many goodbyes. How lonely must you be, Doctor? Join us."

"I could save everyone," the Doctor whispered.

"Yes," Finch agreed.

"I could stop the war."

"No," Sarah Jane said firmly, stepping forward. "The universe has to move forward. Pain and loss, they define us as much as happiness or love. Whether it's a world, or a relationship, everything has its time. And everything ends."

"I promised you once, and I'll promise you again," Jessie added, looking at the Doctor when he stared at Sarah Jane in shock. "There will always be me. Remember? How long I'll stay with you? I promised it, and I'm not breaking it. Forever."

The Doctor looked at her then, and something shifted behind his eyes. He grabbed her wrist, and she shrieked, but he simply turned her wrist, pointing the gun at the big screen with the code flashing across it, and he fired at it, smashing it. "Out!" he shouted.

Jessie took her cue to run, the others following her. She heard the sound of a car revving and the smashing of the glass doors of the school. A few minutes later, she almost ran into Saleen, FitzSimmons, and a boy she remembered from the cafeteria, Kenny. "What's going on?" Jemma asked.

Jessie just kept running. They made to the canteen area when the doors banged open. Jessie looked over her shoulder as Finch and more Krillitanes approached. Kenny's eyes widened. "Are they my teachers?" he asked in surprise.

"Yeah," the Doctor replied. "Sorry."

"We need the Doctor alive," Finch declared. "As for the others? You can feast."

FitzSimmons and Sarah Jane dove with Kenny under the tables. Jessie, Saleen, and May began firing as the swooping Krillitanes, occasionally ducking to avoid being grabbed. A laser beam hit one of the Krillitanes, and Sarah Jane grinned. "K9!" she cried.

"Suggest you engage running mode, mistress!" the robotic dog replied.

"Come on!" the Doctor called to them. Jessie ran past him, opening the doors as the Doctor called to K9. "K9, hold them back!"

"Affirmative, master. Maximum defense mode!"

"It's the oil," the Doctor panted as they made it to the physics lab he and Jemma had "taught" in. "Krillitane life forms can't handle the oil. That's it! They've changed their physiology so often, even their own oil is toxic to them. How much was there in the kitchen?"

May smiled. "Barrels of it."

The Doctor grinned back at her. "OK. We need to get to the kitchens. Saleen - "

"What now?" she complained. "Hold the coats?"

The Doctor shook his head. "Get all the children unplugged and out of the school. FitzSimmons, help her out. Now then . . . " He looked up as the Krillitanes began banging on the doors. "Bats, bats, bats. How do we fight bats?"

Kenny solved the problem by pulling the fire alarm. The Doctor grinned at the boy and ran out of the room, right past the Krillitanes. "Master," K9 reported as he caught up to them.

"Come on, boy!" the Doctor encouraged. "Good boy!"

***

Jessie and May began hauling the barrels into position as the Doctor tried to open them. "They've been deadlock sealed," he said, sounding frustrated. "Finch must've done that. I can't open them."

"The vats would not withstand a direct hit from my laser, but my batteries are failing," K9 noted.

"Right." The Doctor clapped his hands. "Everyone out the back door! K9, stay with me."

Jessie, May, and Sarah Jane ran out the back door as the Doctor hauled the rest of the barrels into position. "Capacity for only one shot, Master," K9 said. "For maximum impact, I must be stationed directly beside the vat."

The Doctor paused, looking at his dog in shock. "But you'll be trapped inside!"

"That is correct."

"I can't let you do that!"

"No alternative possible, Master."

The Doctor knelt down and patted the dog. "Goodbye, old friend."

"Goodbye, Master."

He gave one last smile. "You good dog."

"Affirmative."

He exited through the back door and sonicked the door. Sarah Jane stared at him. "Where's K9?"

"We need to run," the Doctor replied, grabbing her arm and pulling her with him.

"Where is he?" Sarah Jane shouted. "What have you done?"

"Let's go, let's go!" Saleen shouted somewhere off to the side as they joined the crowd of kids running. "Come on, guys! Run!"

The school exploded behind them, and the kids began to cheer. Jessie and May seemed to get what had happened the same time Sarah Jane did, because she began to cry. "I'm sorry," the Doctor apologized.

Sarah Jane shook her head. "It's all right. He was just a daft metal dog." She sniffed. "It's fine, really."

The Doctor simply hugged her as she burst into tears and buried her face into his shoulder.

***

"Cup of tea?" the Doctor offered Sarah Jane, opening the door of the TARDIS.

Jessie looked over from where she was talking to Saleen. "May's reporting back to Coulson," she explained. "They'll be leaving in a few hours."

"You've redecorated," Sarah Jane commented, looking around.

"Do you like it?" the Doctor asked.

"Oh, I . . . I do," she replied, nodding. "I preferred it as it was, but, er . . . yeah. It'll do."

"I love it," Jessie said with a grin.

"Not much like the Bus, but it's home," Jemma agreed, smiling.

"Speaking of the Bus," May said as she came back from the TARDIS corridor. "Coulson's there already."

"That'll be our cue," Fitz said.

"Wait a moment," Sarah Jane interrupted, pointing to Jessie. "You. What's forty seven times three hundred and sixty nine?"

Seventeen thousand, three hundred and forty three. Jessie blinked when the answer stayed in her head. What the hell? "No idea," she lied, panicking a little. "It's gone now. The oil's faded."

"But you're still clever," Sarah Jane grinned. "More than a match for him."

"You and me both," Jessie laughed. "Doctor?"

"Er, we're about to head off, but you could come with us?" he offered.

Sarah Jane smiled softly and shook her head. "No. I can't do this anymore. Besides, I've got a much bigger adventure ahead. Time I stopped waiting for you and found a life of my own."

Saleen shuffled. "Can I come?" Jessie jerked her head towards Saleen, followed by the rest of the SHIELD team there and the Doctor. "No, not with you," she told Sarah Jane quickly. "I mean . . . with you." She nodded to the Doctor. "Because I'm not the tin dog. I want to see what's out there."

"Oh, go on then, Doctor," Sarah Jane encouraged. "You've been talking about how you like gingers. Maybe it's time you had a ginger onboard."

"OK then," the Doctor agreed, and Jessie chewed her lip, trying to ignore the flare she felt in the pit of her stomach. "I could do with a laugh."

Saleen looked at Jessie worriedly. "Jessie, is that OK?"

"No," she replied quickly, knowing that she was really lying through her teeth. "Great. Why not?"

Sarah Jane stepped over to her, smiling. "Well, I'd better go."

"What do I do?" Jessie whispered as she stopped by her. "Do I stay with him?"

"Yes," Sarah Jane confirmed. "Some things are worth getting your heart broken for." Jessie smiled and gave the woman a huge hug, which was returned. "Find me, if you need to one day," Sarah Jane whispered in her ear. "Find me."

***

The Doctor followed Sarah Jane, May, and FitzSimmons outside. "It's daft," Sarah Jane said, "but I haven't ever thanked you for that time. And like I said, I wouldn't have missed it for the world."

"Something to tell the grandkids," the Doctor joked.

"Oh, I think it'll be someone else's grandkids now."

"Right. Yes, sorry. I didn't get the chance to ask." The Doctor tilted his head. "You haven't? There hasn't been anyone?"

"Well," Sarah Jane said slowly. "There was this one guy. I traveled with him for a while, but he was a tough act to follow." Jemma grinned at the look on the Doctor's face. Sarah Jane did, too. "Goodbye Doctor."

"Oh, it's not goodbye," the Doctor began to protest.

"Do say it," Sarah Jane begged. "Please. This time. Say it."

The Doctor nodded slowly. "Goodbye, my Sarah Jane."

Jemma stepped forward after the Doctor gave Sarah Jane a hug big enough to lift her off of her feet. "Doctor," she said lowly as she made it to his side. "You better tell Jessie sooner or later, because I get the feeling she's not as happy as she should be with Saleen onboard now."

The Doctor frowned, looking at her. "What?"

Jemma punched him in the arm. "You know it, because you were going to say it after you fixed K9," she hissed, and something flashed in the Doctor's eyes, and he looked down almost in embarrassment. "Saleen said after we met Sarah Jane that you were just like any other guy. There were only one in Jessie's. One made her life living hell, but the other helped her rebuild hers, and now they're both dead. Don't be the first kind of guy."

The Doctor nodded, hugging her. "I promise."

"Take care of them, Doctor," Fitz said, walking up next.

The Doctor shook his hand. "Fizzy boy."

Fitz grinned. "I'll let that pass this time."

"Keep on flying, Agent May," the Doctor told May, giving her a hug as well.

May nodded. "I plan on it."

The Doctor went back into the TARDIS, and it began to dematerialize. Sarah Jane and May began to walk away, but Jemma kept watching. When it faded away entirely, her eyes widened when she saw what had been left behind. "Oh my God!" she gasped. "Sarah Jane!"

She turned back immediately, and her eyes brightened. "K9!"

"Mistress," the dog replied, rolling towards her.

"But you got blown up!" Fitz protested.

"The Master rebuilt me," K9 explained, and Jemma grinned. "My systems are much improved with new undetectable hyperlink facilities."

"In other words, he replaced you with a brand new model," Jemma summed up.

"Affirmative."

Sarah Jane smiled. "Yeah, he does that." She began walking off with the other four. "Come on, you. Home. We've got work to do."

"Affirmative."

"Sarah Jane?" May called, and Sarah Jane stopped to look over at them. "If you ever do need a job, give us a call."

Sarah Jane nodded. "I will. Agents."

Jemma smiled as Sarah Jane and K9 left. "The Doctor was right," she said.

"On what?" Fitz asked.

Jemma beamed. "Brilliant." She looked up to the sky as she quoted him. "'Good for you, Sarah Jane Smith.'"

***

I love K9. "You bad dog." "Affirmative." *sniff* Poor dog.

How do you think it's going to be with Saleen on board? Is she going to be like Mickey? Better? Worse?

And how the hell did Jessie know that answer?

Whaddya think? Next up will be the interlude, followed by The Girl in the Fireplace.