"Well, it worked," said Zac. "But why? I don't understand. What do you want with me?"

The Dark Lord's head shifted just a fraction in his direction. "You?" he said. "Why would we want anything from you? I was talking to him." He turned his head towards Angelo.

Angelo and Zac exchanged a puzzled glance.

"Me?"

"Him?"

"Why did you want me?"

"You are unique, Angelo," Satan said. "One of a kind, almost certainly never to be repeated. And that makes you important. And it makes you fascinating." He gestured around at the stark walls and spotless worktops. "All this is for you, Angelo. We built the tenth circle for you, so that we may... get to know you better. Because you are special, my boy. Half angel and a" drumroll, please a" half demon."

"I know that," Angelo said.

Satan missed a beat. "Oh," he said. "Right. Do you?"

Angelo puffed out his pigeon chest. "My dad told me."

"Ah," said Satan. "Well, that's disappointing. I was looking forward to revealing that." He paced round the metal frames that held both boys, examining Angelo from all angles.

"You've spent such a long time up there," he said. "Now it's time you joined us down here for a while and indulged your dark side."

Angelo frowned. "What?"

The Dark Lord was interrupted before he could reply by the sound of a ringing phone. Eliza, the hunchbacked demon with the liquid bottle, flipped open a handset and pressed it to her ear.

"Yes?"

She listened intently, watched by the other four people in the room. After a moment, she moved the phone away from her ear.

"It's the fourth circle, sir. About the hot pokers. They're asking should they go through the eyes or up the bottom?"

Satan tapped a finger against his chin as he considered this. "Why not both?"

The hunchback nodded, spoke the instruction into the phone, then snapped it closed.

"Where was I?" Satan asked. He rocked back on his heels. "Ah, yes. Put him in the chair."

At that, everything seemed to grind into slow motion. Zac saw Haures lunge for Angelo, heard Angelo cry out in panic and fear. Shapes moved in the corners of Zac's eyes. He turned and saw a dozen or more demons in surgical clothing swarming towards the reclining chair. Had they been there the entire time, or was there a door behind him? A way out? An escape route? He twisted his neck, trying to see, but all he saw was white wall and silver worktop, and all he heard were Angelo's squeals as Haures unhooked him and carried him over towards the chair.

"What are you doing with him?" Zac cried. He pulled at his chains, but they held fast. "Let him go. Leave him alone."

Angelo was bucking and thrashing in Haures's arms, kicking out with his bare feet and biting at anything that came within reach. He shouted angrily. He pleaded and sobbed. He tried everything he could to stop them putting him in that chair, but then he was on it, and then he was strapped in, and then he was trapped.

The demons in the surgeon outfits chittered excitedly behind their masks. Their dark eyes swept over Angelo, appraising him even as their gnarled hands rubbed together with glee.

"The book."

Zac tore his eyes from Angelo. The Dark Lord stood beside him, a heavy leather-bound book balanced on the palm of one hand. A small padlock and strap fastened the pages closed. On the cover, the words: THY BOOK OF EVERYTHING glowed faintly in shades of gold.

"What, you're just giving it to me?" he asked.

Satan shrugged. "I don't want it. It has served its purpose. Keeping it would start a war, and that's the last thing anyone needs."

"You've already started a war," Zac told him. "If you don't let Angelo go, they'll send an army."

"Will they indeed?" said Satan. "We'll see."

He walked behind Zac and unzipped the backpack. The book was shoved roughly inside before the zip was fastened once more. Zac looked back at Angelo. Something like an oxygen mask had been slipped over his face, but the gas flowing in through his mouth and nostrils was a dark, brooding red. Angelo's eyes were bulging, staring up at the ceiling, but he was no longer fighting against the straps.

Satan appeared in front of Zac again. "Don't worry. We'll take good care of your friend." He tapped himself on the forehead. "Wait, I forgot a" he isn't your friend, he's your colleague. Isn't that right?"

Zac didn't reply, just kept watching the boy in the chair.

"You have what you came for, Zac Corgan. You can return a hero and have all your sins washed away. Play your cards right and you'll never have to see me again." He smiled thinly. "And won't your grandfather be pleased to have you home?"

The mention of his grandfather made Zac look Satan's way. The Dark Lord's face became solemn. "Anyway, he was miserable up there. No friends. All alone. And that tattoo? Horrible. Who's to say he won't be happier down here with us? With his daddy and all his aunts and uncles and brothers and sisters."

Zac could feel the demon inside his head, twisting his thoughts and fogging his brain. "I'm... I'm not leaving without him," he hissed. "I'm not leaving him here."

The Dark Lord Satan, Father of All Lies, Angel of the Bottomless Pit, nodded. "Oh, but the thing is," he said, "you don't have any choice."

Then he smiled and snapped his fingers. The room around Zac began to fade. He saw Angelo's head loll sideways to look at him. "Don't go," the boy wheezed. "P-please."

"I'll come back!" Zac shouted. "I'll get help and come back. I promise!"

Then the room faded completely, and Angelo was abandoned to all the demons of Hell.

AC FELL FORWARD, the chains no longer round his ankles and wrist, and so no longer holding him up. He landed awkwardly on hard-packed sand and lay there, face down, until the inside of his head stopped spinning.

When he finally got up, Zac found himself standing beneath a pale blue sky. The sand stretched out around him in all directions, flat on his left, hills and dunes to his right.

There was no wind. Not a breath of air moved across the desert. He turned in a slow circle, sweeping his gaze out over the sand. There were no demons, no Angelo, no chair and no straps. He was, as far as he could tell, completely alone.

"Great," he muttered. "Now what?"

He walked a few paces in one direction, stopped and walked back. He looked around again, but the landscape was still devoid of life.

Then he remembered the watch. Gabriel had said he could use it to contact Heaven once he had the book. He looked at the little screen. Where the time should have been was a question mark, and a basic animation of a stick man shrugging his shoulders.

Zac studied the watch more closely. It had four buttons along one side and two on the other. One of them, he imagined, would allow him to call for a rescue party. But which one?

There was a flash of light and a puff of smoke and the hunchbacked demon, Eliza, popped out of thin air. She stuck her tongue out at him, then smashed a little pointed hammer against the watch face. With a sharp giggle she vanished again, leaving Zac staring blankly at the broken timepiece on his wrist.

"Well, that's just great," he sighed, before a tennis ball hit him hard on the back of the head.

He turned, fists raised, head throbbing. The ball had come from the direction of the dunes. And now he was paying closer attention he could hear noises a" voices, maybe a" from behind the closest hill. He listened, and soon the voices were joined by the sound of heavy footsteps on the compacted sand.

A large man with a long, flame-coloured beard trudged into view at the top of the dune. He stopped when he saw Zac. There was a long moment in which he and Zac just stared at each other in silence, but then the man cupped his huge hands round his mouth and shouted, "Chuck us the ball back!"

Zac looked down at the tennis ball by his feet. It was grubby and weather-beaten. Someone had scribbled a large number 4 on it in black marker pen. Zac picked it up, then approached the man on the hill.

The closer he got, the bigger the man seemed. He stood almost as tall as Haures had. His beard was easily a metre long itself, and his muscles bulged beneath the leather armour he wore. The giant watched Zac impassively as he trudged up the hill.

"Who are you?" Zac demanded, stopping in front of the man.

"Who are you?" he replied in a thick Scottish accent.

"I asked you first."

The man reached over his shoulder. His fingers wrapped round a long handle, and there was a shnink of a blade being unsheathed.

"Well, I've got a big sword," the man scowled. "And it's dead sharp."

Zac weighed up his chances. He'd taken down plenty of adults before, but none as big as this one. He was holding the sword like he meant it too. It was not a fight Zac wanted to have.

"Zac Corgan," he said. "Now your turn."

The big man glowered down at him. "War," he said.

"War?"

"Aye," said the giant. "War."

"As in... battles and fighting and stuff?"

"As in the Horsemen of the Apocalypse."

Zac considered this. He looked War up and down. "Yeah," he said, willing to accept pretty much anything at this point. "Course you are. Where're the other three, then?"

"Coo-ee!" came a voice from beyond the brow of the hill. "Get a move on. We haven't got all day, you know?"

War sighed and closed his eyes. "You had to bloody ask."

A skinny man dressed all in white scurried the last few steps up the dune. He wore a floppy sunhat on his head and thin rubber gloves on each hand. He gave a soft gasp when he spotted Zac. "Oh, hello," he said. "Who are you, then?"

"Zac Corgan, Pestilence," growled War. "Pestilence, Zac Corgan."

"Lovely to meet you," beamed Pestilence. "And I love the whole black-outfit look. Very mysterious."

War sighed. "Right, give us the ball back."

Zac handed it over. "What is this place?" he asked.

"It's Limbo," said War.

"Limbo?"

"Which probably means you've died, I'm afraid," added Pestilence. "So please accept our condolences."

"What's keeping you?" asked a voice a little way down the dune. A boy just a year or two younger than Zac marched to the top of the hill. He had an oversized plastic baseball bat in one hand. "I need to get back home soon or my mum's going to..."

The boy's voice trailed off. "Who's this?" he asked.

"Drake, this is Zac," Pestilence said. "Zac, Drake here is our latest Death."

"Latest?"

War grunted. "Long, boring story."

"Zac has recently died," Pestilence continued. "Isn't that a shame?"

"No, I haven't."

Pestilence smiled gently. "Yes, you have," he said. "I know it's hard, but the sooner you accept it, the sooner you can move on."

Zac shook his head. "No, I haven't. I was sent on a mission to find a stolen book. I was in Hell a minute ago, and now I'm here."

War and Pestilence exchanged a glance. "The Book of Everything?" Pestilence asked in a hushed voice.

"Book of Everything, Book of Doom a" take your pick," Zac said. "I found it, but they kept my... colleague. It was all a trick to get him down there."

Pestilence's mouth tightened. "That's them all over, that is," he said. "Always up to something. I'm sure he'll be OK, though."

A snort of laughter came from War. "Oh aye, I'm sure he'll be just dandy. They're a right fun bunch down there, just ask anyone."

There was a moment of uncomfortable silence.

"That was sarcasm, by the way," War pointed out.

"Still, at least you found the book," said Pestilence. He clapped his hands. "Yay!"

"You brought it back to them yet?" War asked.

"No. I got stranded here. I've got no way of contacting them." He looked at the Horsemen in turn. "Unless you've got some way of getting in touch with Heaven?"

"We'll go one better," said Drake. "We'll take you there ourselves." He looked from Pestilence to War. "Um... we can do that, right?"

Zac stood in the shadow of a small wooden shed and gazed up at its jolly red roof. There was a creak from the door as Drake pushed it open. Zac hung back as War and Pestilence stepped inside.

"A shed?" he asked. "Why are we getting in a shed?"

Drake smiled. "Just trust me."

"No."

"Oh," said Drake, a little deflated. "Right. Well, the shed can travel across dimensions or... or something like that. It can fly you to Heaven."