"Good. And what else? Do you recall what I said the first time I showed it to you?"

Toby thought back.

"You said it was the... engine?"

Harris clapped his hands together and rubbed them briskly.

"Exactly!"

"So if this is the Ark's engine, then the Gnarl at the centre of the Bubble Belt..."

The old man gave an encouraging nod. "Go on."

"The Gnarl at the centre of the Bubble Belt is also an engine?"

"Excellent, Toby! Excellent." Harris slapped him on the shoulder. "Now come here."

The Professor led Toby over to a Grid terminal that had been patched into the table. With a few deft touches, he brought up a computer rendering of the Bubble Belt: a shell of billions of spherical habitats surrounding the gas-wreathed Gnarl at its centre.

"The Belt," he said.

Toby leaned forward. The diagram was a crude schematic, but it was sufficient to provoke a pang of homesickness. Shaking it off, he pointed to the Gnarl at the centre, represented by a spherical white dot.

"You're not telling me that this thing's an engine for the whole Belt?"

"That's exactly what I am saying. Watch this."

Harris tapped a couple of controls and the simulation changed.

"Now look closely. Once activated, the Gnarl flares like this." On the screen, a pencil-thin beam of blue light lanced from the object. Where it passed, the orbiting habitats drew aside, staying clear of the beam.

"But the acceleration," Toby said. "Won't it leave the bubbles behind?"

The Professor shook his bushy head. "Not at these speeds. Remember, we're talking about moving something with the mass of a solar system. The accelerations involved are minute, a few tenths of a gee at most."

Toby rocked back on his heels.

"But why would you want to move it?" he said, feeling he had missed a crucial point.

Harris gave him a sharp glance.

"Oh, use your head, boy. Why do you think? What possible threat could the Dho have foreseen when they were building the Belt?"

"The Dho built the Belt?"

"Well, of course they did. Who else goes around using Gnarls as engines?"

Toby put his hand to his chin. "Then they must have wanted to move it because of The Recollection."

"A fair assumption."

"But they already have their Ark."

Harris gave another irritated shake of the head. "Obviously, the Bubble Belt isn't for them."

"Then who is it for?"

"For us, of course. It's a lifeboat, Toby. A lifeboat for humanity. That's why they built the arch network, to get us off Earth. They linked it to every human-habitable planet they could find. The clues were all there in the carvings. They wanted us to spread out, in the hope The Recollection would miss a few of us here and there, that somehow we'd survive. And they wanted some of us to find our way to the Bubble Belt, so we could join them in their exodus; so that they'd know for certain they'd saved at least some of us."

Toby could feel his heart pounding against his ribs. He glanced down at his shirt, half-expecting to see the fabric moving in time to each beat.

He reached out and brushed the image of the accelerating Bubble Belt.

"Surely that's too slow? How can that outrun anything?"

Harris crossed his arms, tweed rasping against tweed.

"The Belt's expected to take a few years to reach its optimal cruising speed."

"What happens if we're attacked in the meantime? What happens if The Recollection finds a way to move faster?"

The old man glowered.

"Have you heard of Socrates, Toby? He was an ancient Greek philosopher, the teacher of Plato. One of his most important maxims was the phrase 'All I know is that I know nothing.' If we are truly ready to learn, to question every assumption we've previously relied upon, then the Dho will be ready to teach us."

"And what will they teach us?"

Harris held up a crooked finger.

"That there is a way to hold back the darkness while we escape."

Toby blinked. He thought for a moment. "In the carving, the ships covering the Ark's retreat were shooting beams of light at oncoming cloud."

"Yes, the Dho call it the 'Torch That Burns The Sky.'"

"They still have those weapons?"

"They do."

Toby's heart surged. "And we can use them?" For a weightless instant he imagined outfitting a ship and jumping to Djatt in time to save Katherine from the encroaching menace; even though in his heart he knew he'd arrive too late, that whatever she'd faced, whatever had befallen her, would be long over and done by the time he got there.

"No," Harris said, cutting across his thoughts. "Humanity must have its champion. The Dho tell us there is a man coming. He is a pure-born Earthman. He has travelled a long way and he is trying to atone for great misdeeds. He alone will operate the weapon."

CHAPTER THIRTY-THREE.

COLD EQUATIONS.

Ejected from the simulation, Kat sat up on her couch. She moaned. Her head ached and the burn mark on her chest stung beneath its dressing.

> Are you okay? the ship asked.

She put a hand to her brow. "I think so."

On the couch beside hers, Victor lay with his eyes still closed. He looked older with his face slack and grimy, and lacking the 1950s sunglasses he'd worn in the simulation: old enough to be her father, maybe even her grandfather. For a dizzying moment, she realised how defenceless he was. She could reach over and use her metal hand to crush his larynx before he regained consciousness. Even if he did wake, he wouldn't have the strength to break her grip.

The Kilimanjaro flashed into her mind. The Abdulov ship that never arrived, whose sabotage had set in motion this whole sorry chain of events. Had he really been involved in its destruction? Lying there on the co-pilot's couch, he looked so spent and helpless that, for the first time, she entertained the thought that the explosion on board the missing ship might have been an accident after all, and her subsequent encounters with Victor an unfortunate twist of fate. Granted, his exit from Strauli Quay, jumping from within a sealed bay, had been a risky, reckless and illegal maneuver-but no-one had been hurt. Similarly, the bomb blast on the Ticonderoga-the one that killed Enid-had been the work of Seth Murphy, Victor's First Mate, and he had received a bullet in the head for his efforts.

That killing was the only one she could definitely attribute to Victor, the man now lying here beside her, and it had seemingly been enacted in punishment for the bomb. She had nothing but supposition to link Victor to either that explosion or the one on the Kilimanjaro; and that wasn't enough for her to pass a death sentence on a sleeping man.

She looked into the face of the man she'd once loved hard enough to abandon her family for, the father of her unborn child, and realised she'd lost the rage that had sustained her from Tiers Cross. It had gone. With the appearance of The Recollection, things had changed. The universe had become a darker and more terrifying place, and her bruised pride had ceased to seem all that important. Not even her family honour mattered anymore, because down on the surface of Djatt, people were dying in their millions. There was no-one left to trade with, only an unimaginable horror to be avoided; a contamination to be stopped. She knew that theoretically she could kill Victor here and now-against the holocaust outside, what would one more death matter?-and yet deep inside, she also knew she lacked the will to go through with it. Instead, she gave his shoulder a gentle shake. After a moment, he coughed. She helped him sit up, and he looked around the bridge, blinking and rubbing his eyes, obviously disorientated.

"What happened?"

"Something went wrong with the simulation," she said, feeling awkward. "The Recollection took control. I think it tried to hack our brains."

Victor's eyes widened. Kat put what she hoped was a reassuring hand on his forearm.

"Don't worry," she said, "we're okay. The ship pulled the plug."

At that moment, as if on cue, the Ameline chipped in.

> Memory core isolated and flushed. Whatever it was trying to do, I stopped it.

Kat said, "Can you eject the core?"

> Already done and dusted. And just to make certain, I fired it through our main engine exhaust. Crisped it up nicely.

"And what of the infected ships?"

The Ameline connected to her implant, superimposing over her vision a tactical view of the surrounding volume. The two infected ships were marked in red. One she recognised as Victor's ship, the Tristero. The other was a freighter from the planet Icefall: an old rust bucket travelling under the given name Hesperus. Both were under thrust, moving away from the planet on divergent trajectories, and neither were answering the Ameline's hails. As she watched, the Tristero flashed white and disappeared. Seconds later, the other ship did likewise.

> Both ships have jumped.

"And they're definitely heading for Strauli?"

> Only the Tristero. As far as I can tell, the other's going for Inakpa.

Kat looked at the roiling blood-red cloud now enveloping most of the planet beneath her. Lightning flashed in the atmosphere. She thought again of her home, and the carnage that would ensue should this horror fall upon it.

"We have to stop them," she said.

Victor sat forward. "And how do we do that?"

"Thanks to you, I came prepared for trouble. I have six nuclear-tipped missiles in the hold."

She enjoyed his whistle of surprise. His eyebrows went up and he gave a nod of appreciation.

"Very nice. But we can't chase both. Which do we choose?"

Kat drew herself up in the pilot's chair. "We're going after the Tristero. We have to stop The Recollection spreading to Strauli."

"What about the people on Inakpa? Can't we warn them?"

Kat felt something harden inside. Perhaps it was her heart. She said, "Inakpa will have to take care of itself."

She brought up navigational data files on both planets.

"There are only six million people on Inakpa. There are over ten times as many on Strauli. And besides, the Quay's a major hub. If this infection gets loose there, it'll have access to dozens of ships, and it'll spread faster than we can stop it."

She glared at Victor, daring him to disagree. He looked unhappy, but nodded all the same.

"Okay," he said. "But the Tristero's engines are bigger than yours. It can reach Strauli in a single jump. Can you?"

Kat closed her eyes, running calculations. She thought of Napoleon Jones and the different ways he'd taught her to push the envelope.

"If we run them at maximum tolerance, they'll make it," she said, with as much confidence as she could muster.

Through her implant, she felt the ship's mind stir uneasily.

"Of course, they'll need an overhaul and refit afterwards."

> If they don't explode first.

"They won't explode."

She called up the navigation systems and selected Strauli Quay.

Victor still looked unhappy.

"Are you sure about this?" he said.

Kat didn't look round. When she spoke, there was an edge in her voice.

"This is my ship. If you don't like what I'm doing, you can always get off." She gestured at the planet below. "Just say the word."

Victor shook his head.

"It's not that."

Kat pulled up the menu of options that controlled the ship's engines, and fed in the necessary safety overrides.