Unick carried Aviel into Carcharon after dark. The drumming was now so loud that it shook the stone beneath their feet, and it appeared to be beating inside his head as well, each thump wobbling his bloodshot eyes in their wet sockets.

“It’s here!” he said thickly.

The place was littered with splintered timbers and fragments of copper roofing, some melted. There was a large ice-filled depression in the floor, as if the stone had softened long ago, then had been moulded like jelly. A warped stone stair ran down into darkness.

The walls were deformed as though parts had flowed and set again, and there was a strangeness about the whole tower that she could not fathom. It was different each time she looked at it, and from the corner of her eye things seemed to shift, as if Carcharon wasn’t quite of this world. It was the most unsettling place Aviel had ever been.

Now desperate for drink, Unick broached the first of the kegs by driving his fist into the top. He tilted the little barrel and gulped a cupful of raw spirit, gasping.

“Aaahh!” he gasped. “Good grog.”

He left her to search the nine-sided tower, but soon returned. “Where… is… it?” he bellowed.

For the next few hours he huddled in the icy depression, drinking until he was almost mindless, his filthy pack beside him. The ends of his three devices protruded from its open top. Every so often black flares radiated from the dark crystal in the tip of Command.

“Power is flowing from the stone,” he said to himself, “but where is it going?”

The Merdrun are taking it, thought Aviel. They’re getting ready to invade. She could not work out exactly how many weeks had passed of the original eight, but it must be close to six.

An owl flew in and circled under the broken roof. Unick fired two ragged blasts at it with Command, though he was shaking so wildly that there was little chance of hitting it. A single pinfeather spiralled down, as if the owl had dropped it to taunt him, then it flew out.

“Death bird,” he croaked. “Lives in haunted places. Comes to remind me I’ve got to pay.”

She felt sure he was right; she kept seeing wispy figures slipping in and out of the walls. Ghosts, watching Unick. They paid no attention to her.

“Where… is… the… summon stone?” he roared.

He took another pull at his barrel, hefted it onto his shoulder and staggered down into the lower levels. She heard him blundering about, cursing and gasping and crashing into walls, then there was silence.

He thought that finding the source would ease his torment, but Aviel suspected his troubles would double the moment he located it. And hers too. The stone had drawn him here from a hundred miles away, and not for his benefit.

She sat down to think things through. She had been shying away from the obvious for ages because thinking about such things was foreign to her nature, but it was time to face it. Unick would never allow her to destroy the summon stone, yet that was the point of everything she had done since reading Malien’s letter. He was planning to feed her to it.

So she had to kill him first.

The quickest way would be to steal his knife when he was dead drunk and cut his throat, though Aviel felt sick at the thought. It would live with her for the rest of her life.

But at least it would be quick. If she did it right it would disable him within seconds. But what if her nerve failed and he caught her? What if she made a mess of it and failed to kill him?

The drumming in Unick’s head was so loud that Aviel could hear it all the time now. He was out of his mind from it.

“Where is it?” he screamed.

He staggered up the steps, hefted the second barrel onto his shoulder, turned to go down again but slipped on a broken piece of stone and the barrel flew out of his hands. It crashed down the steps, slammed into the wall and broke open.

Unick howled and hurled himself after it. He lay on the landing, lapping at the dusty stone until his tongue bled, but less than a cup of muddy spirits remained. The rest had soaked into the cracks between the stones and disappeared.

“Where is the summon stone?” he shrieked.

Nothing else could ease his torment, which was worse than ever now that he had no way of staying drunk. Unick was trembling so violently that he could barely walk; he kept throwing up blood and seeing nightmare visions. He stalked up and down, pointing his Origin device in every direction, fruitlessly trying to locate the summon stone in the maze under Carcharon.

He came crawling up the stairs, gasping and holding his belly. “Aftersickness. Worse than… ever felt. This… a poisoned place.”

Aviel said nothing.

“Potion!” he snapped. “Give it here.”

She handed him the phial with the thread tied around it.

Unick studied it suspiciously, then shook the last of the Eureka Graveolence, two drops, onto his filth-encrusted palm.

“That’s way too much,” said Aviel. “It only takes a sniff.”

She caught a whiff of burned bones and felt a throbbing pain behind her temples. Unick snorted a drop up each nostril. The drumming roared; his feet pounded up and down, then he convulsed so violently that he turned an involuntary backwards somersault and hit the floor.

He got up, clutched at his belly and heaved, but he had eaten nothing in a week and all he brought up was blood streaked with green bile. He wiped his mouth on his sleeve and laughed maniacally.

Taking Aviel by the wrist, he jerked her so violently that it felt as though her arm had come out of its socket, then dragged her down the steps. She went thumping down on her bottom, her bad ankle twisting under her. He descended four levels, struck the wall with the side of his fist and a section swung open. He went through into darkness.

He released her; she heard a sizzling sound and blue light throbbed from the Origin device. He shone it around in all directions, the flaring light picking his features out from below. He looked demonic.

Unick caught her wrist again and continued down, following a tortuous path through a myriad of passages. Aviel, fearing that she would never find her way out, surreptitiously dripped scent from one of her belt phials, then another.

“Shh!” he said.

Now his movements became exaggerated, caricature-like. Aviel could no longer hear the drumming, though she could hear a repetitive rasping, as if one stone was sliding over another. A circle of dark red light appeared, outlining a deep shaft or well. She could not see anything at the bottom.

Suddenly Unick caught her about the waist and leaped into the shaft. Aviel screamed. His free hand slapped across her mouth and nose. He landed on a projecting block a yard down with a thump that rattled her teeth, sprang to another block around and down from the first, then another and another.

The shaft was like a spiral staircase with most of the treads missing – any misstep and they would plunge fifty feet to the bottom. He hit the floor hard, staggered through a stone slot, hauled her around a U-shaped bend and into a long gloomy chamber lit by a dull red glow. The nearer end of the chamber was lobed, like an arm ending in stubby fingers.

Unick thrust Aviel away from him and she fell to a stone floor, though it was not paving, as the upper levels of Carcharon had been. Here the stone appeared to have been eaten away.

“It’s here,” he whispered. “It’s here!”

The glow brightened to a crimson radiance, outlining something near the far end of the chamber. And the summon stone was nothing like she had expected.

Malien had said to smash it to bits and burn the pieces, so Aviel had expected a small rock, a crystal or a stone artefact.

But it consisted of three tall slabs of stone, each seven feet high and two feet across. Two of the stones were upright and touching, while the third lay across their tops to form a closed trilithon, one with no space between the uprights. A deep red light ebbed out from the core of the stones, washing everything in the chamber blood red.

“The source!” sighed Unick.

He picked Aviel up, crushing her face into his reeking armpit, carried her to the three-lobed cavity at the other end of the chamber and tossed her into the middle lobe. Turning back towards the trilithon, he drew the Command device from his rucksack.

“Don’t use mancery near it!” cried Aviel.

He pointed it at the trilithon. “I command —”

The crimson light flared and he was hurled back against the wall. He rose shakily, made an adjustment to the device and tried again. Again it flung him back. He made another adjustment and tried a third time. This time the trilithon flared so brightly that Aviel was dazzled. When she could see again Unick lay on the floor, unconscious, and the Command device was in a dozen pieces, though she felt sure he could put it back together.

She had to act quickly; he no longer needed her.

Smash it and burn the fragments. But Aviel was afraid to go near the trilithon, and her hammer was useless. Even if she’d had a sledgehammer, she would not be able to break such massive stones. How could it ever be destroyed?

Feed it!

It was a harsh, alien voice – female, she thought. Aviel shuddered. Was it the magiz Karan had seen?

Unick got up and dragged her towards the trilithon, smiling dreamily. Had the summon stone taken control of him? She struggled but he was far too strong. This was it, she thought with a dreadful calm – she was going to die.

The trilithon flared and the drumming began again, so deep that the three stones vibrated against one another and the walls of the cavern shook.

He stopped six feet away, tremors racking him and sweat forming puddles around each filthy foot. She sensed that he was afraid, that the summon stone was nothing like he had expected either. He raised her above his head. She tried to kick him in the face but could not reach.

“It has to be fed,” he said, and hurled Aviel at the trilithon.

She was trying to cover her face with her arms when she struck an invisible membrane that depressed under her weight and sprang back, catapulting her at Unick. Her shoulder struck him in the throat and he went down, choking.

She crawled away. What had just happened?

Feed it!

“What with?” gasped Unick.

Start with a finger.

He drew his knife and headed after Aviel.

Not… corrupt… enough. Your finger!

Now, for the first time since she had met him, Unick showed fear.

“But I’ve helped it to wake. And look what it’s cost me.”

First a finger, best given in terror.

He retreated, slipped in his oily sweat and fell to one knee, then pushed himself up to a kneeling position and raised his hands. The palm of his left hand was bloody. He looked down at it, then up at the trilithon. His face was distorted, his little eyes starting out of their red sockets. He slowly put his left hand on the floor and extended his little finger.

“Don’t do it,” said Aviel.

Unick slammed the knife down on his finger, severing it. He bared his teeth, picked the bloody finger up and in a swift movement tossed it at the trilithon. It burned to smoke before it reached the surface, and the smoke was drawn to the point where the three stones met.

The drumming, which had been sounding all this time, cut off. Unick toppled over and lay on his side, his knees drawn up. Blood dribbled from the stump of his finger. His eyes were open and staring, though he did not seem able to move.

But Carcharon now seemed disturbingly alive and only tenuously connected to the rest of the world. What was it connected to?