Happy looked at JC. “Don’t ever ask me to do that again. There aren’t enough pills in the world to flush that woman’s thoughts out of my head. I may put in for compensation for post-traumatic stress disorder.”

“You were born with that,” said JC.

“True.”

And then they all stopped talking to look at Kim as she advanced slowly but remorselessly on Erik. He backed away, clutching his cat-head computer to his chest. There was something new about Kim, something different, and disturbing. As though she wore the cold presence of death like a cloak. Erik swallowed hard as Kim drifted down the platform after him.

“What . . . what do you want?” he said, his voice catching in his throat. “I’ve been good. I’ve done everything that’s been asked of me.”

“Put down the computer,” said Kim.

Erik clutched the machine tightly. “No. It’s mine. I made it. I dreamed it up. I made it real.”

“Put down the computer,” said Kim. “While you still can.”

Erik looked into her eyes, and whimpered. He put the box down on the platform and scuttled quickly backwards. Kim knelt and peered into the cat head’s unblinking eyes. It tried to purr for her.

“Poor little kitty,” said Kim. “No more screaming, no more crying. Sleep.” She extended her ghostly hand down through the cat head and into the glowing workings of the box beneath; and the whole computer shuddered. It turned and twisted unnaturally, imploded, and was gone in a puff of displaced air. The cat’s head was left behind on the platform, quite dead. Kim smiled and turned back to face the others.

“It’s at peace now,” she said.

Melody looked at JC, but he stopped her with an upraised hand.

“Work your equipment,” he said. “Find me the answers I need to take the fight to the enemy. I want this over with.”

He walked off down the platform, and Kim drifted after him. They tried to walk arm in arm, but their arms kept passing in and out of each other.

Unknown to all the agents in the Underground, there was someone else down in the station with them. Lost and alone, little Billy Hartman went scurrying through the empty corridors like a rat in a sewer. Not very big, never very big, Billy stuck to the shadows, hiding behind corners and peering warily through entranceways. No coat, only a grubby sweater and stained jeans, and a pair of knock-off trainers that had never been fashionable. Half out of his mind with fear and panic, driven on by rage and resentment, tormented by horror and loathing for the awful thing he’d done, little Billy spied on all the other people from a safe distance. None of them noticed him, but then, no-one ever did. He was far too small to be noticed by such powerful people.

And besides, Billy was protected.

He heard them speak, heard them argue, heard of the Carnacki Institute and the Crowley Project; but these names meant nothing to him. He listened to the great people, as they spoke of theories and fears and intentions, and didn’t care about any of that, either. He only had thoughts for himself and what might become of him. He’d done something, something big and important that no-one could ever put right again. If they knew, if they only knew . . .

The day before, Billy Hartman had murdered Kim Sterling. Even though he had no real reason, no motive, no idea who she was. He’d never killed anyone before, never really wanted to. He wasn’t a murderer, wasn’t a beast or a monster. He was a little man with a little life and less ambition. A small cog in a small wheel in a small company that no-one else gave a damn about. But he woke up that morning with murder on his mind, and he couldn’t seem to shift it. He wanted to kill a beautiful woman . . . like all the ones who’d laughed at him, or spurned him, or worse still, ignored him. He wanted to hurt one of them the way they had hurt him. To strike back, just once, and let them feel the pain.

So he took a big knife from his tiny kitchen in his shabby little flat and went out into the great big world, humming cheerfully. He descended into the Underground, and travelled up and down the lines, switching from platform to platform until finally . . . he saw her. And knew immediately that she was the one. He’d thought it would be a hard thing, a difficult thing, to actually kill another human being; but when the time came, he walked up behind her, stabbed her once in the back, and walked away. No-one saw or suspected him. Why should they? He was far too small and unimportant to be noticed. He went back to his flat, still humming cheerfully, made himself a meal-for-one in his little microwave, watched television, and went to bed.

To dream of how it felt when the blade went in, and he twisted it, before withdrawing. He didn’t enjoy it. It felt like someone else’s dream.

But this morning, a new feeling had driven him from his bed. The feeling that something had gone wrong. The morning news said that Oxford Circus Tube Station had been shut down, and serious news presenters said the word murder in their serious voices. And suddenly Billy knew he had to go back, that he had to go back down into the Underground and make sure there was no evidence left to link him to the crime. He couldn’t have anyone finding out what he’d done. That would be awful.

Sneaking back in had proved surprisingly easy. On any other day the massed forces of uniformed police and security guards would have intimidated him into a frozen panic; but not that day. He walked right past them, and they never saw him. Partly because he was, after all, a small and insignificant person, but also because Someone was looking out for him. He could feel it. Someone big and powerful was protecting him.

He walked right past them, right under their noses, and they couldn’t see him.

But once he was down in the tunnels, moving in scurrying little runs through the fiercely bright light, from shadow to shadow and hiding-place to hiding-place, things happened that destroyed what little confidence he had. Bad things. Billy saw bad things. He saw ghosts and monsters and horrible, impossible things, nightmares broken loose and running wild in the world; and he ran and ran until finally he saw the worst thing of all. The ghost of the beautiful woman he’d killed the day before. She looked just as beautiful, dressed in white like an angel, her hair the same colour as the blood that had spilled down her back when he pulled out the knife.

He crouched, in the deepest and darkest of the shadows, watching her with wide, confused eyes, scared out of his mind. He didn’t feel guilty, and he didn’t feel sorry; he knew now he’d only done what he’d done in the service of his Protector. But he was terrified that these big and important people, with their big and important voices, would tell the authorities what he’d done, then everyone would know. He’d be caught and punished and locked up in a cage, forever and ever. Billy had gone through most of his life afraid of being punished.

First, he spied on JC and his team, then he spied on Natasha and Erik, trying to figure out who they all were and what they were doing. Trying to figure out what he should do. He saw them do amazing and awful things, then he saw them fight each other, and he saw them working together. None of it made any sense to Billy. The ghost was there, too, acting like she was still alive; and once she turned her head and looked right at Billy. He shot off immediately, running and running and not looking back, and when he finally stopped to glance fearfully around him, he was on a platform he didn’t recognise.

He moved slowly, diffidently, down the platform. He was meant to be there. He could feel it. His unseen Protector had brought him there, for some important purpose. A train pulled into the station, moving smoothly and silently—a dream of train, come just for him. Billy made ooh and aah noises. The train was painted in bright colours, from end to end, all the fresh and vivid shades of childhood. A great big toy train, just for him. Bright and cheerful and not threatening at all. (So why were all the hairs standing up on his arms and the back of his neck?) The Protector had sent this train, the Protector who had hidden him from the authorities, who loved him and cared for him and looked after him. Who now called to Billy in the sweetest of voices, calling him . . . to come and meet his Protector, and get his reward for killing the beautiful woman.