Paul drew breath to yell, but the Infected moved first, slapping a hand over his mouth.

A warm hand.

Something in that touch killed the terror inside him. It was a human touch. Skin and blood and flesh. Realization slotted into place.

Caitlyn.

The thing that had been Caitlyn saw the recognition in his eyes. She shrank back from him, withdrawing her hand, averting her face as if ashamed. Her straggly hair hung over the machine half of her features, a curtain to cover them up. Paul couldn’t help the horror and revulsion he felt at the sight of her, but he managed to keep from showing it.

This is Caitlyn. Don’t look at the Infected part. This is Caitlyn, and she’s as scared as you.

He swallowed. It was hard to overcome the fear of infection, knowing that the merest scratch could end his life. He didn’t know how much of her was the girl he’d known and how much was the nanomachines now. She might lash out at him at any moment.

His skin tingled unpleasantly where she’d touched him. Just your mind playing tricks, he told himself. He hoped so.

They faced each other on their hands and knees, confined by the tunnel. Two rats in a maze, both searching for a way out.

“Caitlyn,” he said quietly. “I’m sorry. I’m so, so sorry.”

Her human eye welled up, and she pressed a finger to his lips. His instinct was to pull away from her touch. He made himself stay. After a moment, she pulled her hand back. She ducked her head and looked away, unable to hold his gaze. Even changed as she was, he knew she had something to say, something she could barely manage to force out.

When the words came, it was a synthesized wheeze so strange that he almost didn’t understand her.

LOVE … YOU …

Of all the things he’d expected to hear, that had been the last. He just stared at her. He felt like he should say something, but nothing came.

I KNOW … YOU … DON’T …, she said. She finally met his eye and held it. HAD … TO …

Out of the turmoil of emotions he felt in the wake of her words, one emerged, like an iceberg breaching the surface of a stormy sea. Pity. Pity so sharp and terrible that it could cut him or crush him.

You didn’t deserve this. You didn’t deserve any of it.

But she didn’t want his pity. There was nothing he could say that would make anything any better. So he said the only thing he could think of.

“Adam’s trapped. He needs our help.”

She gave him the faintest of smiles, grateful that he’d changed the subject. It was the least he could do for her.

SHOW … ME….

“Adam,” Paul’s voice called quietly through the grate.

Adam hadn’t moved from his warm spot by the radiator. He was quite relaxed, considering. There was something about that Paul kid, a manner that reassured him. He was a decent guy, Adam had decided. Not the kind who’d run off and leave you.

It had crossed his mind that Paul had given him the hardest job on purpose, sending him down into the basement just out of spite, or some kind of revenge for their past fights. But that was stupid, of course. He might have believed that of other people, but not Paul. He didn’t know why. Paul just didn’t seem to be like that.

Besides, he’d come all the way down here to help Adam out, hadn’t he? And since he’d managed that much, Adam had faith that he could pick up a wrench from somewhere.

“Do me a favor, Adam. Turn off your light for a minute.”

Adam frowned at him, narrowing his eyes. That old suspicion stirred. He didn’t like to be made a fool of. “What for?”

“Just trust me, okay?”

Adam considered that for a moment. He did trust Paul. So he stifled the urge to ask any more questions, reached over, and turned off the flashlight.

In the darkness, he heard shuffling. Movement in the air duct. Someone crawling.

Why would Paul ask him to turn the light off?

There was a screech of metal. Adam jumped. He scrambled for his flashlight, picked it up, found the press-button, and turned it on.

The grate covering the air duct had been ripped free from the wall, the metal slats mangled as if crushed by some incredible force. He stared at it. Faintly, from the shaft behind, he could hear a noise, a breathy mechanical sound like someone sighing through an out-of-tune harmonica. And he heard Paul say something in response.

“Paul?”

Warily, Adam crouched down and shone his light up the air duct. Paul was at the end, squashed up at the junction. He was looking off in another direction. There was the sound of someone moving quickly away down the shaft on their hands and knees, but it wasn’t Paul.

“Someone in there with you?” he asked.

Paul looked over at him and beckoned. “Come on,” he said.

Adam squeezed himself into the shaft and crawled toward him. He didn’t like not knowing what was going on. It made him suspect that a nasty surprise was in store.

“Follow me,” said Paul. “The ducts come out fairly near the stairs. I think we can sneak the rest of the way from there.”

“How’d you do that with the grate?” Adam asked.

“I’ll tell you once we’re out of here,” said Paul. “Right now, we’ve got to hurry. Really hurry.”

“Why? What’s gonna happen?”

There was a strange look on Paul’s face. Worry. Fear. Sorrow? Adam wasn’t good at reading people. Whatever it was, he was looking off up the air duct again, but when Adam looked there was nothing there.

“I don’t know,” Paul said. “All I know is, we’d better not be here when it does.”

Erika stood on the edge of the sports hall roof, hugging herself against the blustery wind. Behind her, she could hear Mark and Carson tinkering and clattering as they fixed up the engine of the helicopter. Carson was still woozy and had a darkening bruise on his forehead, but he hadn’t stayed unconscious for long. Johnny was elsewhere, sitting on his own, obsessed with his own thoughts. Just as Erika was.

The campus was quiet. The Infected had stopped shrieking some time ago, their grief and anger spent, and gradually they’d dispersed and scattered. The occasional Infected still wandered about here and there. She’d seen some heading off toward the lake and the old ruined chapel. Others ambled aimlessly around the tennis courts at the far north end of the campus. The few that were left had been easy enough for Mark and Johnny to avoid on their way over from the school.

The Infected seemed to have lost their direction now. Perhaps their appetite for recruiting new victims had run out. Whatever the reason, they were apparently content to stay inside the campus walls and drift about. Erika occasionally caught sight of one of the creatures absorbing another, but mostly they did nothing.

She wondered why they didn’t leave. If they broke out through the gates, they could spread over the countryside. Perhaps they didn’t want to stray too far from each other. What was it Radley had said? They’re smarter when they’re together? And something about an Alpha Carrier? Maybe it was that which kept them here.

Are they just waiting around while the network builds? While they get smarter and evolve? Maybe they’ve used up all the resources nearby.

It sickened her to think of people as resources, but that was how the Infected must have seen them. Hosts. Carriers. Raw material to be processed.

Caitlyn.

No. She wouldn’t think about Caitlyn. Not now. She needed to be strong.

She felt in her pocket for her cigarettes, found them, and then patted about for her lighter. It wasn’t there. She remembered it had fallen out of her hand in the swim hall. Too much trouble, she decided; she put the cigarettes back.

“Those things’ll kill you,” Paul had told her once. The thought brought a tiny smile to her face. She remembered him grinning at her on the rooftop of another building, the science block, which was still burning nearby. The wind down the valley carried the smoke south and away from her.

Paul, she thought. Where are you?

Mark and Johnny had told her how Paul had gone down into the basement after Adam. It seemed like the kind of stupid heroics she’d often scoffed at in the movies that Tom liked to take her to. Pumped-up jocks running through a hail of bullets to save their buddies. When she saw it in the cinema, from the luxury of her nice safe world, it had always seemed laughably dumb.

But this was no movie. The world was no longer nice and safe, and she didn’t laugh at things like that anymore. She didn’t think Paul was stupid. She thought it was the bravest thing she’d ever heard.

I did my part, she thought. Now you do yours. Get out of there alive.

She turned away from the edge of the roof and walked toward the chopper. Mark and Carson were just closing up the engine compartment. Mark got up and grinned at her.

“Done,” he said.

“It’ll fly?”

“She’ll fly,” said Carson. “Not gonna know for sure if everything’s alright till we get her up in the air, but I’ve checked everything. I’m as certain as I can be.”

“Shouldn’t you try out the engine or something first?”

“Last time I started those blades spinning, every Infected in the area went for us. Might be they haven’t noticed us up here yet, but as soon as I fire up that chopper, they’re gonna come running.” He clapped his hands together. “So I want everyone in. Let’s get to it.”

Mark looked puzzled. “You just said —”

“Right,” said Carson. “Once we turn on that engine, we’re taking off. So let’s get her going. Won’t be a second chance.”

Mark looked to Erika for support. “But …” Then his expression hardened. “Paul and Adam aren’t back yet.”

Carson gave him a sympathetic look. “They ain’t coming back.”

“They’ll be here,” Mark insisted.

“If them creatures come swarming at us, how long you think we’ll have, huh? They can climb walls now. It’s only a matter of time before they notice there’s four juicy humans up here. I ain’t going out like Radley did.”

Mark’s hands had bunched into fists at his side, and his normally weak chin had gone firm. “They’ll be here!”

Someone banged on the roof hatch, making them all jump.

“There!” said Mark. “See?”

Mark ran over to the hatch. Muffled voices were calling from beneath. There was a heavy metal box full of flight equipment lying on top of it, which they’d taken from the chopper to stop anything coming up from below. Mark heaved at it, and Johnny joined him.

“Careful!” said Erika. “What if they’re —”

But they’d already shoved the box aside, and pulled up the hatch.

Mark’s face fell as he looked inside. Erika felt a cold dread touch her.

Infected? Please, no. Not when we’re so close.

And then two kids scrambled up through the hatch and onto the roof. One skinny, one fat. They looked around excitedly, then both exclaimed, “Yeah!” and they fist-bumped.

Freckles and Pudge.

“How … er … how did you … ?” Mark was saying. He was fighting to conceal his disappointment.

Freckles shrugged. “Hid in a cupboard till they were gone. Sneaked out under cover of the smoke while they were all going crazy afterward.”

“Just like Metal Gear Solid!” beamed Pudge, his chubby cheeks swallowing his eyes.

Carson was leaning against the side of the chopper. He gave Erika a look, as if to say, Well?

“They’ll be here,” she said.

Carson sighed and looked away.

The door. The door with the blue light.

Caitlyn was finding it hard to think anymore. She loped along the pitch-black corridors of the basement, but they were not pitch-black to her. Her Infected eye glowed blue, and that provided light enough for her amplified senses. Through the blue darkness she went, searching.

She passed other Infected. She didn’t fear them. They didn’t acknowledge her.

The whispers in her subconscious were louder now, but they really weren’t like whispers at all. No words. Just … knowing. And with each passing minute this new way of thought was taking her over, replacing the clumsy connect-the-dots intelligence of humankind.

She was not alone anymore. No longer would she be left to pick her way through life, making her own path to revelations. She was suspended in a cloud of knowledge, and she was everywhere within it.

No, she thought. Not yet.

She struggled to keep her mind on track. She was human, human, human. And there was one thing she had to do before she could rest.

Love you.

She’d heard herself say it, the words mangled by her new vocal cords. What must he have thought, hearing those words from her, seeing her like this? But it didn’t matter. She’d told him. That was enough.

The thought sharpened her mind. She found the door she was looking for. The door with the blue light. She opened it and stepped into the boiler room.

The nanos had removed the fear from her, in order to ease her change. That was good. Without it, she might not have managed to enter that place, that infernal, steaming stew of black pipes and lurching metal bodies.

She moved warily inward. The presence of the Alpha Carrier was impossible to ignore. Though she could only see it as a shape in the fog, she was uncannily aware of it. It was more solid, more real, more there than any of the other Infected. It was important to her.

Important to the Infected, she told herself. Not to me.

Why was she here again? Oh, yes …

She moved among the heating tanks and pipes, reading the old stamped-iron signs there. PUMP CONTROL. STOKE HOLE. STEAM RELEASE. Lantern-eyed metal creatures slunk and shifted around her. She saw the Alpha Carrier pick up a runty Infected and crunch it down. After that, she made sure to stay far away.

She drifted, lost focus. It felt like slipping back into sleep when you were trying to get out of bed. She only knew she’d done it when she found herself on the other side of the boiler room, not sure how she’d gotten there. It alarmed her. Soon there would be nothing left of her, and only the Infected would remain.

One thing to do before that. Just one.

She concentrated, searched, and found what she was looking for. The main gas valve that fed the boiler. A metal turn-wheel projected from a thick pipe that came from the ground. She rolled it; it turned easily, driven by the strength of her metal limb.

There was a series of whuffing sounds as the boilers went out. All across the vast hall, the growling sound of gas flames died. After half a minute, all that was left were the eerie ticks and groans and creaks as the tanks cooled.

The Infected paid no attention. They ignored what she was doing. It didn’t matter to them whether the heating was on or off.

Now, she thought. Now.

It felt bad. It felt wrong. At first she couldn’t even bring herself to do it. Something was stopping her, some instinct. The Alpha Carrier! What about the Alpha Carrier?

She gritted her metal teeth, and forced out all the hatred she could manage. She thought of all the things she could have done in her life. All the joy she might have experienced. She might even have won over Paul, given time.

But the Infected had taken that away from her.

So she turned the wheel again, all the way open.

Sssssssssss …

The hollow, throaty hiss of gas.

She stepped away from the valve. It was not fear she was feeling now, but some other emotion, somewhere between guilt and disgust and self-loathing, something that begged her to undo what she’d done. But she wouldn’t. She moved off between the tanks, into the blue mist.

Gas, hissing from a thousand holes. The gas burners beneath the vast tanks. Once they were turned on, the operator was supposed to press the ignition to light them, just like a burner on a stove. Perhaps there was even some automatic safety system hidden among all this ancient Victorian pipework that would trigger the ignition automatically.

But there was no electricity. So the ignition couldn’t spark. And the gas kept coming.

Everyone who’d been at the academy long enough had heard the story of Billy McCarthy. The boy who’d died down in the boiler room, choked by gas. And everyone had heard about the janitor who went down into the gas-filled basement the next morning, and came a hairbreadth from blowing up the entire school.

She reached into a pocket with her human hand and took out what was inside.

Erika’s lighter.

A sense of unease stirred across her consciousness. A swirl in the cloud. She was not fully part of the network yet: It didn’t know her mind, couldn’t process her human thought. But in their vague way, the Infected sensed danger.

The creatures stirred as the room began to fill with gas. There was a sense of disquiet in their shuffling movements. Violent squabbles broke out here and there. The Alpha Carrier shifted its enormous body with a clattering of metal, as if discomfited.

The air became sharp and choking and it stank, but the Infected didn’t notice. She wondered if they could smell it at all. Many of them didn’t even have noses, and those that did had metal ones.

Caitlyn began to get light-headed. She felt herself slipping, her thoughts becoming fuzzy, and she bit her lip hard enough to bleed. The pain brought her back. If she let go, if she let her Infected side take over, she’d go back and turn off the gas. She had to keep control.

Think, she told herself. Think of anything. Anything but what you’re about to do.

What came to her was netball.

She remembered the game they’d played that morning. She remembered Soraya’s smiling face, Soraya, who’d thankfully gone home for the weekend and hadn’t been caught up in this yet. Oh, Soraya, I hope you’ll be okay. And she remembered Erika, Erika as goal shooter, receiving a pass from Caitlyn, coming to a halt, then her long limbs stretching as she popped another ball through the hoop.

Except in her memory there was no resentment, no hate, no sour jealousy in her heart. There was only the joy of the game, the pleasure she took in the way they worked together, how they’d pass and move their way up the court, cutting through opponents like a hot knife through butter. Caitlyn, making the plays from the center of the court. Soraya, racing along the wing. Erika, on the spot to finish it off.

And so what if Erika took the glory? So what if she had the final shot? She’d never have even gotten there if not for Caitlyn and Soraya and the others.

We made a good team, she thought. We really did.

She clutched the lighter tight in her fist. Erika’s lighter. She remembered Erika’s tearful face, as she was pinned against the wall, a metal claw around her throat. “What did I ever do to make you hate me so much?” she’d asked.

Nothing. Nothing at all. It was always Caitlyn’s problem, all along.

She heard a hiss nearby, a hiss louder and more sinister than the gas leaking into the room. She looked up, her vision blurring as her human and Infected eyes fought for dominance.

One of the Infected was looking at her. Looking right at her. A tall, scrawny nightmare of a thing with a face of warped metal. Ripped overalls clung to its body. A janitor’s clothes.

And as she stood there, another one nearby turned to her. Then the one next to that. She heard a shifting and a crashing of metal, and turned that way.

Across the length of the chamber, two huge eyes were staring at her through the mist. The eyes of the Alpha Carrier.

They know, she thought. They’ve sensed it at last.

She raised Erika’s lighter, cupped it with her metal claw and held it up in front of her face. There was no fear. They’d taken it away. That was their mistake.

The Alpha Carrier screeched, and every Infected in the chamber howled at once, a noise like a hundred jet engines in a hurricane. They leaped toward her, gnashing, screaming, racing to tear her apart.

For us, she thought, and sparked a flame.

After that, there was only light.