Looking casual was difficult.

They'd had to huddle together over the entrance to block her from view. It was better that the tourists saw nothing... though, with this in mind, it did seem oddly suspicious that two teenage boys and a teenage-looking girl were standing shoulder-to-shoulder next to the tomb like guards.

But thankfully for them, most tour groups just ignored them. A few people glanced apprehensively and kept walking. They turned away quickly when either Leo or Emilia grinned. At first, Leo had made a comment that it was because they were Mexican. Emilia made a gesture over her face, reminding him that she looked like a serial killer. His argument stood because he didn't think he looked like one, which must mean the stares were for another reason.

The trio of Americans were still in the room, glancing at them ever so often. Why they lingered, Emilia didn't know. She didn't think they were here for a good reason. The sooner Hazel came back, the sooner they could get away from those men.

"So," said Frank abruptly, making both Leo and Emilia flinch. "Um, well, Leo, Hazel told me you figured out about my lifeline."

"Lifeline?" asked Emilia.

Hesitantly, Frank admitted, "My life is tied to this piece of firewood... Juno revealed it to my mother and grandmother when I was a baby and I've known it was my weakness ever since. If the stick ever burns up, I'll die."

She winced, finding it a cruel way to balance out his incredible abilities. "Look, man," said Leo, knowing Frank was most wary of him, "I'd never do anything to put you in danger. We're on the same team."

Frank fiddled with his centurion badge. "I always knew fire could kill me, but since my grandmother's mansion burned down in Vancouver...it seems a lot more real."

Leo hesitated. "Your grandmother—did she die in that fire? You didn't say."

"I—I don't know. She was sick, and pretty old. She said she would die in her own time, in her own way. But I think she made it out of the fire. I saw this bird flying up from the flames."

"Does everyone in your bloodline have this power?" asked Emilia curiously.

"I guess," said Frank. "My mom did. Grandmother thought that's what got her killed in Afghanistan, in the war. Mom tried to help some of her buddies, and... I don't know exactly what happened. There was a firebomb."

Leo winced with sympathy. "So we both lost our moms to fire."

Emilia was silent as Leo told Frank the story of how his mother died in the workshop when Gaea appeared to him. She felt out of place there, given her mother wasn't dead (rather, just wanted to hurt her as far as she knew), but it seemed both of them were comforted by her quiet presence. Leo glanced at Emilia multiple times while telling his story, having already spoken to her at length about it. Even Frank seemed to let his eyes flicker to her, using her as a guide for how he should be reacting.

Frank's eyes got watery. "I never like it when people tell me, Sorry about your mom."

"It never feels genuine," agreed Leo.

"But I'm sorry about your mom."

"Thanks."

Hazel still wasn't back. Frank continued, "Back at Camp Jupiter, our cabin Lar, Reticulus, told me I have more power than most demigods, being a son of Mars, plus having the shape-changing ability from my mom's side. He said that's why my life is tied to a burning stick. It's such a huge weakness that it kind of balances things out."

"Nemesis and her games," muttered Emilia. "Balance... it's both a wonderful and terrible thing. This piece of firewood, where–?"

"With Hazel," said Frank. "I trust her."

Leo tried to lighten the mood. "We've all got weaknesses. Me, for instance. I'm tragically funny and good-looking."

Frank snorted. "You might have weaknesses. But your life doesn't depend on a piece of firewood."

"No," Leo admitted, his eyebrows furrowing as if he was coming up with an idea. "I wonder..."

"Guys," said Emilia suddenly, noticing the three American tourists were making a beeline for them. "They're coming right for us."

The Americans' faces were angry and confused, like they were sleepwalking through a very annoying nightmare.

"Leo Valdez," called the guy in the ROMA shirt. His voice had changed. It was hollow and metallic. He spoke English as if it was a second language. "We meet again."

All three tourists blinked, and their eyes turned solid gold. "Oh, not you again," said Emilia, bringing the shadows to form a shield between them. "I wish I could just slice them in half."

"Let's go," said Leo, pointing at the hole. "They can't fit down there."

She covered them as they went in– Frank first, in the form of a snake. Leo jumped in after him. Emilia brought the shadows down to form a barrier over the entrance like a door as she leapt in, the spirits wailing above, "Valdez! Kill Valdez!"

The hatch above them closed automatically, cutting off their pursuers. As the light went out, Emilia reached out to grab them (she waited for Frank to turn back into human form and somehow he still squealed in surprise) making sure they remained linked. "Hey," she said, making Frank and Leo hold each of her shoulders. "Stay connected."

Overhead, the marble floor shuddered– the tourists were probably kicking it. "What now?" asked Frank.

"We'll find Hazel," said Emilia. "Did anyone bring a flashlight? I can lead the way as best as I can but if something comes for us, you two will be at a disadvantage."

"Okay, don't freak," said Leo to Frank. "I'm going to summon a little fire, just so we can see."

"Thanks for the warning."

Leo's index finger blazed like a birthday candle. In front of them stretched a stone tunnel with a low ceiling. Just as Hazel had predicted, it slanted down, then leveled out and went south. They made their way down the corridor, Emilia leading then Leo following with the fire. Frank would hold the rear the best.

After a hundred feet or so, they turned a corner and found Hazel. In the light of her golden cavalry sword, she was examining a door. She was so engrossed, she didn't notice them until Leo said, "Hi."

Hazel whirled, trying to swing her spatha. Emilia blocked it with a shadow before it could whack Leo in the face. "What are you doing here?" demanded Hazel, startled.

Leo gulped. "Sorry. We ran into some angry tourists." He told her what had happened, eliciting a hiss of frustration.

"I hate eidolons," she muttered. "I thought Piper made them promise to stay away."

"Oh..." said Frank. "Piper made them promise to stay off the ship and not possess any of us. But if they followed us, and used other bodies to attack us, then they're not technically breaking their vow...."

"Wonderful," said Emilia distastefully. "We cover our bases next time. Where to now?"

"This door is giving me fits," said Hazel. "Leo, can you try your skill with the lock?"

Leo cracked his knuckles. "Stand aside for the master, please."

The door was interesting, much more complicated than the Roman numeral combination lock above. The entire door was coated in Imperial gold. A mechanical sphere about the size of a bowling ball was embedded in the center. The sphere was constructed from five concentric rings, each inscribed with zodiac symbols—the bull, the scorpion, et cetera—and seemingly random numbers and letters.

"These letters are Greek," said Leo in surprise.

"Well, lots of Romans spoke Greek," said Hazel.

"I guess. But this workmanship...no offense to you Camp Jupiter types, but this is too complicated to be Roman. This machinery is delicate, sophisticated. It reminds me of... It's a more advanced sort of lock. You line up the symbols on the different rings in the right order, and that opens the door."

"But what's the right order?" asked Hazel.

"Good question. Greek spheres... astronomy, geometry... Oh, no way. I wonder...What's the value of pi?"

"Uh." Emilia tried to remember. School had been way too long ago. "3.14159265... and that's all I remember. Is that enough?"

"It should be," said Leo. "If I'm right."

Frank looked nervous. "And if you're not?"

"Well, then, Leo fall down, go boom. Let's find out!" He turned the rings, starting on the outside and moving in, lining up the correct numbers so they made the value of pi. Nothing happened. He paused. "I'm stupid. Pi would expand outward, because it's infinite." He reversed the order of the numbers, starting in the center and working toward the edge. When he aligned the last ring, something inside the sphere clicked. The door swung open.

"Have I told you lately how smart you are?" said Emilia, reaching for Incubo as she led the way through.

"You could do with saying it more often," said Leo smugly. "That, good people, is how we do things in Leo World. Come on in!"

"I hate Leo World," Frank muttered as Hazel laughed.

The room they entered was about the size of the Hephaestus forge back at Camp Half-Blood, with bronze-topped worktables along the walls, and baskets full of ancient metalworking tools. Dozens of bronze and gold spheres like steampunk basketballs sat around in various stages of disassembly. Loose gears and wiring littered the floor.

Thick metal cables ran from each table toward the back of the room, where there was an enclosed loft like a theater's sound booth. Stairs led up to the booth on either side. All the cables seemed to run into it. Next to the stairs on the left, a row of cubbyholes was filled with leather cylinders—probably ancient scroll cases.

Flanking the doorway were two armored manikins— like skeletal scarecrows made from bronze pipes, outfitted with full suits of Roman armor, shield and sword. "Dude." Leo walked up to one. "These would be awesome if they worked."

Frank edged away from the manikins. "Those things are going to come alive and attack us, aren't they?"

Leo laughed. "Not a chance. They aren't complete." He tapped the nearest manikin's neck, where loose copper wires sprouted from underneath its breastplate. "Look, the head's wiring has been disconnected. And here, at the elbow, the pulley system for this joint is out of alignment. My guess? The Romans were trying to duplicate a Greek design, but they didn't have the skill."

Hazel arched her eyebrows. "The Romans weren't good enough at being complicated, I suppose."

"Or delicate," added Frank. "Or sophisticated."

"Hey, I just call it like I see it." Leo jiggled the manikin's head, making it nod like it was agreeing with him. "Still... a pretty impressive try. I've heard legends that the Romans confiscated the writings of Archimedes, but—"

"Archimedes?" Hazel looked baffled. "Wasn't he an ancient mathematician or something?"

Leo laughed. "He was a lot more than that. He was only the most famous son of Hephaestus who ever lived."

"For some reason, I hate knowing about the famous people that were actually demigods," muttered Emilia. "I still haven't been able to forget when Will told me that Shakespeare was a son of Apollo... um, I don't want to doubt you, but how do you know this is Archimedes?"

"It just has to be," said Leo confidently. "I've read all about him. He's a hero to Cabin Nine. The dude was Greek, right? He lived in one of the Greek colonies in southern Italy, back before Rome got all huge and took over. Finally the Romans moved in and destroyed his city. The Roman general wanted to spare Archimedes, because he was so valuable— sort of like the Einstein of the ancient world— but some stupid Roman soldier killed him."

"There you go again," muttered Hazel. "Stupid and Roman don't always go together, Leo."

Frank grunted in agreement. Leo was unfazed, "Archimedes was seriously elite. He calculated the value of pi. He did all this math stuff we still use for engineering. He invented a hydraulic screw that could move water through pipes."

Hazel scowled. "A hydraulic screw. Excuse me for not knowing about that awesome achievement."

"Sorry to cut this short," said Emilia, motioning for them to shut up. "But what does that have to do with this?"

"Anyway," said Leo, "all his inventions weren't enough. The Romans destroyed his city. Archimedes was killed. According to legends, the Roman general was a big fan of his work, so he raided Archimedes's workshop and carted a bunch of souvenirs back to Rome. They disappeared from history, except..." Leo waved his hands at the stuff on the tables. "Here they are."

"Metal basketballs?" asked Hazel, tilting her head.

Leo seemed offended by this. "Guys, Archimedes constructed spheres. The Romans couldn't figure them out. They thought they were just for telling time or following constellations, because they were covered with pictures of stars and planets. But that's like finding a rifle and thinking it's a walking stick."

"Leo, the Romans were top-notch engineers," argued Hazel. "They built aqueducts, roads—"

"Siege weapons," added Frank. "Public sanitation."

"Yeah, fine," said Leo. "But Archimedes was in a class by himself. His spheres could do all sorts of things, only nobody is sure..." He ran to the row of cubbyholes and examined the markings on the scroll cases. "Oh, gods. This is it!" He gingerly lifted out one of the scrolls. "Guys, this is the lost book!" His hands were shaking. "Archimedes wrote this, describing his construction methods, but all the copies were lost in ancient times. If I can translate this..."

"We should've brought a wagon or a bag for you, or something," said Emilia, figuring he'd love to take more things home. "You and Annabeth could probably spend years here examining all this stuff. I still remember the first time she showed me Daedalus's laptop..."

"This is bigger than that!" marveled Leo. "If there's a Roman attack on Camp Half-Blood, these secrets could save the camp. They might even give us an edge over Gaea and the giants!"

Hazel and Frank glanced at each other skeptically. "Okay," said Hazel. "We didn't come here for a scroll, but I guess we can take it with us."

"Assuming," added Frank, "that you don't mind sharing its secrets with us stupid uncomplicated Romans."

"What?" Leo stared at him blankly. "No. Look, I didn't mean to insult— Ah, never mind. The point is this is good news!"

Out of nowhere, one of the orbs on the table clicked and whirred. A row of spindly legs extended from its equator. The orb stood, and three bronze cables shot out of the top. Before anyone could react, they sped into Hazel, Frank, and Emilia's chests like Taser wires. Emilia felt a sharp pinch, then the room went dark.

She heard a loud series of yells and crashes before she was finally able to open her eyes. She sat up weakly as a strange warbled voice– it sounded like an eidolon again– snarled at Leo, swords and shields crashing repeatedly into each other.

"Yeah!" she heard Leo say. "Who's possessing who now, Casper?!" She smelled smoke just before he added, "Guys, take cover!"

Frank reacted fastest, pulling Emilia and Hazel under the nearest table. Emilia lifted her hands, forming a weak barrier of dark energy as an explosion filled the room, the air smelling like a horrible burning engine. When the smoke cleared, she saw Leo grinning down at them, "You're alive!"

"I'm as surprised as you are," said Emilia, the shield flickering away weakly. "What the hell happened?"

"Archimedes came through!" said Leo. "Just enough power left in those old machines for one final show. Once I had the access code, it was easy."

Frank blinked several times. "The eidolons... are they gone?"

Leo grinned. "My last command overloaded their kill switches— basically locked down all their circuits and melted their cores."

"In English?" asked Frank.

"I trapped the eidolons inside the wiring. Then I melted them. They won't be bothering anyone again." He helped them to their feet, locking eyes with Emilia. "Nemesis... isn't so bad."

Her heart sank. "You used it?"

"I had to."

"You saved us," said Frank softly.

"Don't sound so surprised." Leo glanced around the destroyed workshop, purposely avoiding Emilia's solemnly proud look. "Too bad all this stuff got wrecked, but at least I salvaged the scrolls. If I can get them back to Camp Half-Blood, maybe I can learn how to recreate Archimedes's inventions."

"If anyone can figure it out, it's you," said Emilia quietly.

Hazel rubbed the side of her head. "But I don't understand. Where is Nico? That tunnel was supposed to lead us to Nico."

"Oh." Leo furrowed his brows. "Hazel, how exactly were you tracking Nico? I mean, could you just sense him nearby because he was your brother?"

She frowned. "Not— not totally. Sometimes I can tell when he's close, but, like I said, Rome is so confusing, so much interference because of all the tunnels and caves—"

"You tracked him with your metal-finding senses," guessed Leo. "His sword?"

She blinked. "How did you know?"

"You'd better come here." He led Hazel and Frank up to the control room and pointed to the black sword, also made of Stygian Iron. Emilia picked it up slowly.

"Oh. Oh, no." Hazel would've collapsed if Frank hadn't caught her. "But that's impossible! Nico's sword was with him in the bronze jar. Percy saw it in his dream!"

"Either the dream was wrong," said Leo, "or the giants moved the sword here as a decoy."

"So this was a trap," said Frank. "We were lured here."

"But why?" Hazel cried. "Where's my brother?"

A hissing sound filled the control booth.The hairs on the back of Emilia's neck stood up when she saw a bronze mirror on the table was steaming.

Ah, my poor demigods. The sleeping face of Gaea appeared in the mirror. She spoke without moving her mouth, voice echoing through the room, bouncing around so that it seemed to come from the stone walls, too. You had your choice. I offered salvation to all of you. You could have turned back. Now it is too late. You've come to the ancient lands where I am strongest—where I will wake.

Leo pulled a hammer from his tool belt. He whacked the mirror. Being metal, it just quivered like a tea tray, but it felt good to smash Gaea in the nose.

"In case you haven't noticed, Dirt Face," said Leo, "your little ambush failed. Your three eidolons got melted in bronze, and we're fine."

Gaea laughed softly. Oh, my sweet Leo. You three have been separated from your friends. That was the whole point.

The workshop door slammed shut. You are trapped in my embrace, said Gaea. Meanwhile, Annabeth Chase faces her death alone, terrified and crippled, at the hands of her mother's greatest enemy.

The image in the mirror changed. TheyAnnabeth sprawled on the floor of a dark cavern, holding up her bronze knife as if warding off a monster. Her face was gaunt. Her leg was wrapped up in some sort of splint. Emilia's heart sank– Annabeth looked terrified. She'd never seen her so scared.

The others, said Gaea, Jason Grace, Piper McLean, and my dear friend Percy Jackson—they will perish within minutes. The scene changed again. Percy was holding Riptide, leading Jason and Piper down a spiral staircase into the darkness. Their powers will betray them. They will die in their own elements. I almost hoped they would survive. They would have made a better sacrifice. But alas, Hazel and Frank, you will have to do. My minions will collect you and Emilia shortly and bring you to the ancient place.

Gaea's lips curled into a cruel smile. It's a pity Eris won't see it, but she'll be reunited with her daughter when little Emilia serves her purpose. Your demigod blood will awaken me at last, your power will be mine. Until then, I will allow you to watch your friends perish. Please... enjoy this last glimpse of your failed quest.

Leo's hand glowed white hot. Hazel and Frank scrambled back as he pressed his palm against the mirror and melted it into a puddle of bronze goo. Emilia put her hand on his shoulder as the voice of Gaea went silent. A shaky breath escaped Leo, "Sorry. She was getting annoying. Emilia–"

"I know," she said quietly. "My mother... she's not on her side. There's hope. We can win this if my mother is no longer here. If she's returned to Tartarus, we have the advantage, Gaea just doesn't know that."

"It was the fortune cookie," murmured Leo. "When I– when I opened it to save you all... Nemesis left a message for me. She said she'd see it all from home. She must have taken your mother with her. Eris could have reached out to her after your talk."

Emilia nodded, hands shaking. "Okay. Okay, this is good. We just have to get out of here. When we find the others, we'll rescue them and Nico. Come on..." She encouraged them to link hands. "I'll get us back to the surface so we can contact Hedge and get him to bring the ship here."