Following Tara down a narrow alley around to the back of the building, Aurelia could feel trembling. At first, she thought it was her legs. The fear of what she was about to do was getting to her. But as they got closer to a metal door, she realized the ground itself was vibrating.

"Stick close to me, okay?" said Tara over one shoulder.

Shouldn't be too hard, Aurelia thought. Tara was dressed in some sort of shining fabric with light panels that shimmered as she walked. She wouldn't be hard to miss. The girl stopped in front of the door and knocked in a complex pattern, and the panel was immediately opened.

"She be with me," Tara said to a tall youth, who simply nodded and stood back to let them both in.

Dense music played, a steady rhythm beating through the walls of the dank corridor they now stood in, and the light was dim and red. It was like being inside a giant heart. Aurelia could hear nothing but the music. Tara took her hand, leading her down a wobbling set of metal stairs. And then she saw it.

The huge cavern was full of elite teenagers, a writhing mass of colors winding in and out of each other like a nest of snakes. For a moment, it was breathtaking, a constantly changing kaleidoscope of patterns. Music throbbed around her head, and Aurelia felt her body respond, her muscles discovering some innate connection to the beat that surrounded her. She wanted to . . . dance? Was that the word? Tara was looking at her and laughing; she said something, but Aurelia didn't catch it. The girl once more pulled Aurelia by the hand. Threading their way through the crowd took them to a smaller room off to one side.

The music was still loud, but at least Aurelia could hear Tara when she leaned in and shouted to ask if Aurelia wanted a drink. She nodded, and the girl signalled her to stay where she was. Obediently, Aurelia remained rooted to the spot, afraid that she'd be lost. In the web of color that ensnared her, Tara wouldn't be as easy to find as she'd first thought. Thankfully, it was only a couple of minutes before she saw the familiar purple hair and a raised hand beckoning her. They went to a corner of the room.

"Here." Tara pushed a container into her hand. "Listen, there could be someone here to help you. I gotta go talk to some people. I need you to stay here where I can find you again, got it?"

Aurelia nodded, then turned her attention to the container she'd been handed. Tara shook her head and grabbed the cylinder out of her hand. She shook it vigorously, then pressed a small slider on the side before handing it back. Again she told her to stay put before disappearing.

The room was spinning with people, the music seemed to have no end or beginning, and Aurelia wondered what it was like to live this life. To have nothing to fill your days with but music and laughter, parties, drinking. She lifted her drink to her lips, swallowed, and grimaced. It was bitter and citrusy, obviously alcoholic. Not wanting to look any more out of place than she already did, she kept the cylinder in her hand but drank nothing more.

A tall boy dressed in a blinding white suit and wearing glasses that glowed in a series of flashing colors smiled at her from across the room. She smiled back, and his glasses glowed green. Gesturing to the dancers, he nodded at her. Confused for a moment, and then realizing he was asking her to dance, Aurelia thought about agreeing. There was something in the raw energy of the dancers that she wanted to be a part of. But no. It wasn't why she was here. Regretfully, she shook her head, and the boy's glasses flashed red for a second before settling back into their repeated series of hues.

She waited, her legs growing tired from standing. The cylinder in her hand at least made her look like she belonged, but she was beginning to get scared. What if Tara didn't come back? Aurelia had two options: attempt to get out and get back to the hospital, or try to figure out how to get into the rest of the tunnels from this cavern. She decided to go with the second option which included not knowing when she'd get the chance to be down here again, when Tara pulled on her sleeve.

"Come," was all she said, and she set off.

Aurelia pushed her way through the throngs of people, trying to keep Tara's purple hair in sight. A hand snaked out and tried to pull her onto the dance floor, but she drew herself away. A dark curtain covered the far wall, and when she reached it, Tara pulled one side away, revealing an opening. They both entered and stopped. The light in the corridor was bright, and they blinked, letting their eyes adjust.

Tara shook her head. "Come on. He's around here somewhere."

"Who?" asked Aurelia, but Tara was already walking away, and Aurelia had to skip a few steps to catch her up.

The corridor stretched for a hundred yards or so, painted in grim, industrial gray paint, lights flickering from a ceiling lined with pipes. At the end was a T-junction, and Tara looked both ways before deciding on going right. It was a good decision, and a second or so later they saw an open door.

A young guy dressed in gray and black was sitting on top of an upturned steel vat. He jumped down when they entered.

"We be ready," Tara said with a sharp upward nod of the head.

"You be psych," the boy said in return.

Gods, this is ridiculous, Aurelia thought. Placing her fate in the hands of two kids who could barely use understandable grammar. The thought made her smile.

"Be Aurelia," Tara said to the boy.

Aurelia shook her head. "This is Aurelia. Look, can we cut the cool crap? I don't really have time for it, and it makes both of you sound like idiots."

The boy looked amused, and Tara raised an eyebrow. "Fine," she said. "It's not my fault that you're old."

Old? She was what, two, three years beyond these guys. Whatever.

"And what's your name?" she asked the boy.

"No names," the boy said. "You two ready?"

"Two?"

"Yeah, I'm coming with you," said Tara.

"I thought you didn't like the dark."

"I don't, but you're going in, so I thought I'd look while I had the chance. I mean, you're not just a kid messing around; you're serious. Besides, this guy here knows these tunnels inside and out, right?"

The boy nodded.

"He's gonna give us the grand tour, you know, take us around a bit, show us what's there."

Again, the boy nodded. "Give me a minute to get the alarms off the door," he said and disappeared.

"Tara, what are you doing?" Aurelia hissed.

"I had no choice. He wouldn't take just you. Doesn't know you. It had to be both of us or none. I thought this was important?" Tara looked half terrified and half angry, her eyes flashing.

"It is important, but I don't want you to risk anything because of me."

"Neither do I. As far as he knows, we're not risking anything. He's taking us on his little tour. If something else happens, then it happens, right? Maybe he even knows some of these black dudes who let people in and out. I don't know, ask him. But wait till we're already out, or he might not even take us."

Aurelia let go a long breath. Tara was right. She'd done what she could and was even willing to go into the tunnels, too. Aurelia had no right to be angry with the girl, but she was. It was hard enough looking after herself without the added responsibility of looking after a kid.

"You gonna drink that?" said Tara, hopefully.

Looking down, Aurelia realized she was still holding the drink cylinder. She shook her head and handed it to the girl, who drank it down in one go, shivering a little as she swallowed.

"There, now I'm ready for anything," she said.

Aurelia sighed.

The boy came back and told them to follow. At the end of the hall was another of the large metal doors Aurelia had seen outside. Before he opened it, he stopped and turned to the two girls. "It's not as dangerous down here as some people might have told you," he said quietly. "Doesn't mean you should shout and scream or do stupid stuff, right?"

He might be young, Aurelia thought, but he had a definite air of authority about him. There was something in his manner that made her trust him, or at least rely on him to look after her.

"Do what I tell you, and you'll be fine, okay?" he added.

Aurelia and Tara nodded, Aurelia noticing that Tara's face was paler than it had been a few moments ago. The kid was scared.

The boy opened the door, metal hinges screeching.

"The doors all have alarms," he said as he pushed. "But we can override them for a while. We've got an hour or so before it'll kick back in again."

The door opened, he stepped through, and the two girls followed.

There was the smell of cold and damp, a musty scent that reminded Aurelia of storage rooms and one of the few times she'd held a real, paper book in her hands. Water was dripping somewhere, and the painted walls of the tunnel were white and dank. Putting her hand out, she could feel a slimy texture, something long neglected. But it was not dark. Surprisingly, the entire length of the tunnel they were standing in was dimly lit by a series of caged lights placed at intervals along the wall.

"Not what you expected?" The boy laughed.

"Not really," said Aurelia, truthfully. "What is this place?"

The boy strode through the corridor, and Aurelia and Tara followed.

"All of Lunar City is riddled with tunnels," he explained as he walked. "Many of them were used in the building process, since it was easier to pressurize underground caverns and supply oxygen to them than it was to use smaller portable domes during construction."

He ducked his head under a pipe thrusting out of one wall and back into the opposite wall.

"These corridors are necessary. There's a lot of Lunar you don't see. A lot of what you take for granted every day depends on these tunnels."

"Like what?" asked Tara. She sounded grumpy. This trip obviously hadn't been anywhere close to as exciting as she'd thought. By the looks of things, she was worried about her shoes, delicately stepping over puddles on the concrete floor.

"Like water, air, even food," the boy said. "All of these pipes you see around you are pumping something to somewhere. Maybe it's water to a kitchen. Maybe it's air out into the dome itself. The corridors give Workers access to those pipes."

"Workers?" asked Aurelia.

"Sure," said the boy. "There are tons of Workers down here. In fact, most of the Workers in Lunar work in the tunnels. Then the elite never have to see them, right?"

They turned out of the main corridor into a slightly narrower one.

"Are all of the tunnels well lit?" Aurelia asked. Being underground was turning out to be a lot more, well, comfortable than she'd expected.

The boy snorted. "Of course. No point Workers being down here if they can't see what they're doing, is there?"

Fair point. The little tour was nice, but Aurelia needed to get more info. "Is there anyone else down here, you know, except for Workers?"

The boy shrugged and kept moving. "Sure, see some people down here sometimes in the further corridors. You're talking about the guys in black, right?"

Okay, this was a start. "Yeah, I've heard of them," Aurelia said casually. "Who are they, anyway?"

"Dunno," said the boy, leading them into another side tunnel, this one with a single large pipe travelling along the middle of the ceiling. "Criminals maybe, guys who got out. Maybe only sec Workers, but I don't think so. We don't talk to them. Run if we see any, just in case."

He was walking quickly, and Tara lagged, her ornate dress flashing strange colors around the corridor and her shoes obviously unsuited to walking far.

"Think we can take a break?" Aurelia called.

"Yeah, in a minute."

He led them around a corner where they found a small niche in which were several boxes. He sat on one and waited for the girls to catch up and sit down. Tara was breathing heavily, and she groaned as she sat on her box. Aurelia thought she heard her mutter something about her damn shoes, but let it go.

"Alright," said Aurelia, once they were all seated. "It's time to be honest. Can I trust you?"

"Yes," said the boy promptly.

Aurelia looked at Tara, who nodded wearily. "Yeah, you can. He's a friend."

"I need to get out."

The boy sucked in a breath, and his eyes narrowed. "Why? You in trouble?"

"No, I swear to you I'm not, but I know someone who is, and I need to get out to bring him back in," she explained. That was putting it simply, but the kid didn't need the details. "Can you help me?"

Crossing his legs, the boy put his chin in his hand and pursed his lips thoughtfully. A lock of golden hair fell into his eyes.

"Not really," he said after a while. "I mean, I don't know how to get out, if that's what you're asking."

"But you know someone who might?"

"In a way," he said. "Look, I can't guarantee anything, and I can't really help you, but I do have a suggestion."

Better than nothing. "What's that?"

"I can take you to one of the far corridors and leave you."

Tara started at this and was about to interrupt, but he held up a hand.

"Hear me out. If I leave you there, then sooner or later one of those guys in black are going to find you. I'll make sure of it. And that's who I think will help you, if you can persuade him, that is."

Aurelia had suspected as much. "Alright," she agreed. "Let's do it."

"Just to be clear," the boy said. "I can't help you get back in again, and I don't know if these guys will help you or not, but it's the best I've got if you really want to do this."

"I'll take my chances," Aurelia said.

"Fine. Let's go. We don't have much time to get back before the door alarm kicks in again, so I can't take you far."

He hopped off his box and walked briskly away. Aurelia followed, and with another groan, Tara also got up and tagged behind.

As they got closer to what Aurelia presumed was the limit of the dome, the tunnels grew narrower. Every now and again, they passed huge, gulping machines, big white boxes that towered above them in caverns and made belching noises.

"Air purifiers," the boy said.

They walked for fifteen minutes, during which Aurelia became completely disoriented. The boy seemed to know every turn and never hesitated. Tara was limping along bravely, and in a fit of sympathy, Aurelia squeezed her hand.

"I'm not sure why you're doing this," she said. "But thank you."

Tara smiled weakly.

Reaching a junction where two larger corridors intersected, the boy finally came to a stop.

"Here's probably the best place," he said. "Close to the edge, but you'll be easily visible. You'll need to wait here; someone will come to you."

"How can you be so sure?" asked Aurelia, suddenly nervous about being left underground alone.

"Because of this," the boy said with a grin, pulling a small silver ball out of his pocket.

"What's that?"

"Smoke pellet," he explained. "Some of the guys use them on a dare. You throw it, and it makes a bang and fills the corridor with smoke. Then you run like hell to make sure one of those guys in black doesn't catch you. It's, well, I guess it's fun. You know?"

"I see," said Tara, who obviously didn't. "And you thought we were the ones who were psych. Right."

The boy ignored her and handed the ball to Aurelia. "Wait until we're gone. Give us five minutes or so, then throw it hard against the floor. The guys in black don't bother us too much if we're not making trouble, but a noise like this thing will make should bring someone running. Okay?"

"Okay." Aurelia nodded.

She turned to Tara. "Thank you," she said simply.

"No worries." The girl shrugged. "You owe me, remember?"

"I remember," said Aurelia. "Com me when you need something."

"If you even make it out and back in again," Tara replied.

"Yeah, thanks for the reminder." But she could see the girl felt bad, as much as she tried to hide it, so Aurelia leaned in and gave her a hug. "Seriously, thank you. And don't worry, I'm gonna be fine."

"Hope so," said Tara, her voice muffled on Aurelia's shoulder. "Com me when you get back, so I know, okay?"

"Okay."

The boy was already walking away. "Come on," he called to Tara.

The girl with purple hair hurried after him. Aurelia had a sudden thought. How could she com her when she didn't even know her last name?

"Wait," she shouted. "I don't know your family name!"

Tara turned for a moment and smiled. "Hansen!" she shouted before running after the boy. In a second, they disappeared around a corner.

Whoa. Wait. What? No, come on, there had to be plenty of Hansens around; it wasn't an extremely unusual name. A coincidence, right? She'd known Tara was an elite kid, so it shouldn't be surprising that she shared a name with Jonathon. Still, the shock of finding out Tara's last name was enough to occupy Aurelia for the first couple of minutes she was alone.

Alone. Oh, Gods. What the hell am I doing down here? She could hear the hum of the electric lights buzzing; the footsteps of Tara and the boy had long since faded. In her hand, Aurelia felt the weight of the silver ball. Turning it slowly in her fingers, she figured she had a decision to make. Not that it was a big one. Sure, she could try and find her way back to the party she'd left, but she knew she'd never make it. Or she could throw this ball and let one of the guys in black find her. They weren't sec Workers, she was sure. In all her time both on Earth and in Lunar, she had never seen a Worker working out of uniform. No, these guys were something else. She could only hope that they were what she needed.

She sat down in the middle of the crossroads. She might as well be comfortable. The ball was still clutched in her hand. Somehow, she wasn't feeling as scared as she should. But she'd seen a man in black before, hadn't she? Her mind went back to the man who had dropped the envelope for her in the alleyway. This was all connected; she merely didn't know how. She held her hand up flat, balancing the ball on her palm, looking at the way the curve distorted her reflection in the cold, dim light. It really wasn't much of a decision at all.

The others had been gone long enough. Grasping the ball in her right hand, she took a deep breath and threw it as hard as she could onto the ground a few yards in front of her. There was a startlingly loud bang that made her ears ring, and then jets of green-and-black smoke hissed out of the ball. The smell was sulphurous, cloying, and given that sec Worker uniforms were also green and black, Aurelia had a suspicion the device had once been some kind of security smoke bomb.

She coughed as the gray billowed around her, but in the long corridors, it quickly dissipated to no more than a haze against the lights. She waited.