We flee without any real plan in mind. I ask the others, as we run, if they have an idea of the layout of the complex, if they've seen more of it than I have. They all reply negatively. Mark has been to a lab that the rest of us haven't visited, but it wasn't far from zom HQ.

"I've always assumed we were underground," Tiberius says, "because of the lack of daylight. But that's not necessarily the case. We might simply be in the middle of a huge building."

"No," Peder says. "I once heard a soldier grumbling about being stuck down here. Reilly told him to shut up - I don't think they were supposed to mention anything about where we are - but it was too late."

"Then I guess we need to head for the top," I grunt. "Let's look for stairs."

We push open every door that we pass and peer through every window. In the dark glass of one pane I catch sight of my reflection and pause. There's a small red z on my right cheek. I frown, wondering how it got there. Then I recall the clown stroking my face. Shivering, I wipe the mark from my flesh and hurry on.

"Here!" Cathy shouts. She's looking through a round panel of glass in a door. I press up beside her and spot a flight of stairs. I shake the door but it's locked. There's a control panel beside it.

"Time to test our toys," I grin tightly. "Gokhan, you first. They usually press their fingers to the sensor before scanning their eye."

Gokhan holds Dr. Cerveris's fingers up to the panel. There's a small beeping noise. I open my hand and reveal the eye. I roll it in my palm until it's pointing the right way, then rest it in front of the retinal scanner. I have no confidence that it will work now that it's been ripped from its socket, but to my delight there's a second beep and the door slides open.

"Eye, eye!" Tiberius snickers, slipping past me and jogging up the stairs.

It's only a single flight of steps. Seconds later we're on a higher floor, identical to the one below, so we go looking for an exit or the next set of stairs. There are zombies loose on this level too, but they don't interfere with us. They shoot us dark looks and sniff the air hungrily when they catch our scent, but when they realize we're not walking snack boxes, they leave us be.

We find another set of stairs and climb, this time up three levels. Once again we search for a way out. But after a couple of minutes Mark looks through an open door and does a double take. "What the hell...?" he mutters.

"Worm!" Cathy barks. "This is no time for - "

"Shh!" he snaps, and the look on his face tells us this is serious.

Curious, we crowd around Mark and gape, slack jawed, at the hellish drama unfurling within.

It's a massive room, the largest I've seen in the complex. Judging by the TV sets hanging from the walls, I'm guessing it's a relaxation area, a much grander version of zom HQ.

Quite a lot of the staff are here, shoved up against one of the walls. They're surrounded by snapping, howling zombies. But the living dead are only occasionally attacking. They're being held in check by a team of people in hoodies. The zombie masters have wrinkled flesh, an ugly mass of purple patches and pustulant, peeling skin. They have pale yellow eyes, and if their hoodies slipped I know we'd see crops of unhealthy gray hair. I also know that they have no fingernails and their tongues are scabby and shriveled.

They're the mutants I saw in my school, and before that on a visit to the Imperial War Museum. They were controlling zombies the last time I saw them, and they're in command now too, directing the reviveds with blasts of the whistles that hang on strings from the neck of each mutant.

In the middle of the mutants and zombies is the clown, Mr. Dowling. He towers above the rest of them, which is strange, as I didn't think he was unusually tall when I saw him in my cell. Glancing down, I see that he's on stilts, balanced elegantly.

Mr. Dowling is waving his hands above his head, swaying gently, beaming insanely.

"Come on," one of the mutants croaks at the weeping, moaning humans huddled against the wall. "Sing or we'll set the doggies on you again. Sing!"

The other mutants take up the refrain and start to bellow, "Sing! Sing! Sing!"

Mr. Dowling giggles shrilly and twirls his arms like an orchestra conductor. The soldiers, scientists and nurses begin to chant together, having obviously been told what to sing before we hit the scene. They're out of tune, and not all in sync, but the song is unmistakable.

"Jingle bells, jingle bells,

Jingle all the way,

Oh what fun it is to ride

In a one-horse open sleigh."

The mutants screech with delight and clap enthusiastically. Mr. Dowling sighs happily and cups his hands to his heart, then wipes a finger across his cheeks as if to remove tears of joy. A couple of zombies dart forward and drag humans from the crowd. They carve their skulls open and tuck in. The survivors sing another creepy chorus of "Jingle Bells" at the rough prompting of the mutants.

While the doomed humans are singing, Mr. Dowling points at a woman and beckons her forward. She shakes her head, terrified, tears coursing down her cheeks. The clown frowns, then draws a finger across his throat. One of the mutants blows his whistle and a zombie drags the woman out and tears into her.

Mr. Dowling smiles and points to another woman. This one hurries forward, not even waiting for him to beckon. When she's in front of him, his smile widens and he bends over and opens his lips. I expect a stream of spiders to come spilling out, but this time he reaches into his mouth and pulls out a scorpion. It's alive and twisting wildly in his grip.

The clown puts a finger to the woman's lips and taps them. With a gulp, she opens her mouth. He sticks his tongue out, then nods at her to do the same. With a delirious giggle, he lays the scorpion on her tongue, then nods for her to close her mouth. With fresh tears, she obeys his command, then falls away a moment later, coughing and choking.

The mutants cackle and kick the woman. The zombies hiss and a few more dart into the fray and emerge clutching struggling, screaming humans.

Then Mr. Dowling's head turns and he trains his gaze on us. No... not on us... on me.

There's no doubt in my mind that he's looking at me specifically. His eyes burn into mine and his lips twitch as if he's just spotted a dear friend. When the mutants see us, they squeal and dart towards us, dragging zombies with them.

Mr. Dowling makes a high whining noise and they stop instantly. As they retreat, he extends a hand towards me, turns it upside down, then slowly crooks his middle finger, beckoning me forward.

"Not even in your sodding dreams!" I scream, then whirl and race away, not caring if the others follow, not worrying about the direction I'm taking, knowing only that I have to get far away from the clown as quickly as possible, before he takes me into his embrace and turns me into something even worse than one of the walking, undead damned.