“And so,” Mark said grimly, “we fired off a neutron star at the Ring.”

“A spectacular gesture,” Uvarov said. “Perhaps humanity’s greatest engineering feat… But, ultimately, futile. For how could a mere neutron star disrupt a loop of cosmic string? And besides, the Xeelee starbreaker technology was surely sufficient to destroy the star before — ”

“But it didn’t work,” Lieserl said slowly.

Mark had been staring at the sensor ’bot; the squat machine had come to a halt before the chair, its sensor arms suspended in the air. “What do you mean?”

“Think about it,” she said. “The neutron star is heading away from the site of the Ring. And it’s clearly not been disrupted by starbreakers.”

“Yes. So something went wrong,” Uvarov said. “Well, the precise sequence hardly matters, Lieserl. And — ”

It happened in a heartbeat.

The light died. The ancient structure was flooded with darkness.

Louise and Mark left the improvised hospital and found an abandoned house. The house was bereft of furniture, its owners gone to live in the zero-gee sky (but, of course, the zero-gee dwellings were gone now, Louise noted morosely, swept out of the sky by the cosmic string incursion).

Mark quickly created a Virtual diagram in the air: a geometrical sketch of lines and angles, lettered and arrowed.

Louise couldn’t help but smile. “Lethe, Mark. At a time like this, you give me a diagram Euclid would have recognized.”

He looked at her seriously. “Louise, working out the spacetime geometry of a cosmic string is a hard problem in general relativity. But, given that geometry, all the rest of it is no more than Pythagoras’ theorem…

“As near as I can figure out, this is what Spinner is up to.” There was a pair of tubes in the air, glowing electric blue, like neon. “We are flying around a pair of cosmic strings. Now, here are the angle deficits of the strings’ conical spacetimes.” Wedges of air, like long cheese slices, were illuminated pale blue; one wedge trailed each string length.

“Okay. Here comes the Northern.” The ship was represented by a cartoon sketch of a sycamore seed in black. “You can see we’re traveling on a curving path around the string pair, going against the strings’ own rotation.”

Now the seed arced into the wedge-shaped angle deficit glow of one of the strings. As soon as it had entered the boundary it vanished, to reappear instantly at the far side of the deficit.

Mark snapped his fingers. “See that? Faster-than-light travel: a spacelike trajectory right across the deficit.”

Now the little ship-model came arcing back and flickered through the second string’s angle deficit. “Louise, the strings are traveling just under the speed of light — within three decimal places of it, actually. Spinner has the Northern traveling at a little over half lightspeed. The turning curves, and the accelerations, are incredible… The domain wall inertial shielding seems to be working pretty well, although there’s a little leakage.”

Louise nodded. “Right. Which is why the Northern is complaining.”

“Yeah. Louise, the Northern wasn’t designed for this — and neither was our bastardized lash-up of Northern and nightfighter. But there’s nothing we can do. We’ll just have to pray the whole mess holds together until Spinner-of-Rope finishes her joy-riding…

“Anyway, the trajectory she’s following is quite precisely machined… We’re passing from side to side of the string pair in light-minutes, but we’re crossing light-years thanks to the spacelike savings. Louise, I think Spinner-of-Rope is assembling closed timelike curves, from these spacelike trajectories.”

Louise stared at the seed-craft; she felt an impulse to reach out and pluck it from the air. “But why, Mark? And how?”

“I know what a closed timelike curve is,” Spinner said. Again she dragged the ship to a halt and whirled its nose around toward the string; although she was still shielded from the impossible accelerations she felt herself gasp as the Universe lurched around her. “The original mission of the Great Northern, with its wormhole, was to follow a segment of a closed timelike curve…”

Yes. A closed timelike curve is a circle in time. By following a closed timelike curve all the way to its starting point, you would at last meet yourself, Spinner-of Rope… Closed timelike curves allow you to travel through time, and into the past.

Again the nightfighter hurled itself at the cosmic string pair; again Spinner hauled at the waldoes, dragging the ship around. The huge wings beat at spacetime.

She screamed, “How much longer, damn it?”

Spinner, each traverse around the string pair is taking us a thousand years into the past. But we need to travel back through a hundred millennia, or more…

“A hundred traverses,” she whispered.

Can you do it, Spinner? Do you have the strength?

“No,” she said. “But I don’t think I have much choice, do I?”

Lieserl looked around the darkened chamber, confused. The ’bot’s brilliant lantern had been extinguished. Suddenly the walls were dim gray sheets, closing over her head, claustrophobic.

“Lieserl.” Mark’s face loomed before her, erupting out of the darkness; his blue eyes, white teeth were vivid. He moved with nanosecond speed, the slowness of humanity finally abandoned.

Dimly, she was aware of poor Uvarov sitting in the pod. He was frozen in human time, and unable to follow their high speed insect-buzz. “What is it? What’s happened?”

“The ’bot has failed. Lieserl, it was controlled by the ship’s processors. The download link from the ship must have gone down…”

Immediately, she felt that loss of processor support. She felt as if her mind had been plunged into a twilight cavern, echoing; she felt herself drift away.

“They’ve abandoned us.”

“Probably they had no choice, Lieserl.”

I am to experience death, then. But — so suddenly?

Lieserl would survive, of course — as would Mark, as projections on board the Northern. But this projection — she, this unique branch of her ancient consciousness — couldn’t be sustained solely by the limited processors on the pod.

She felt a spasm of regret that she would never be able to tell Louise and Spinner-of-Rope about the wonderful little people embedded inside the neutron star flux.

She reached for Mark. Their environment suits melted away; desperately they pressed their bodies against each other. With deep, savage longing, she sought Mark’s warm mouth with her lips, and -

“Lethe. And we can’t even talk to her.” Louise looked out of the house and across the lifedome, in the vague direction of the nightfighter cage. “Mark, Spinner is a smart woman, but she’s no expert on string dynamics. And she’s out there without significant processor support. I don’t see how she’s even calculating the trajectories we’re following.”

Mark frowned. “I — wait.” He held up a hand, and his expression turned inward, becoming blank.

“What is it?”

“We’ve stopped. I mean, the traverses around the string pair have been halted.” He thought for a moment. “Louise, I counted a hundred and seven complete circuits…”

“Louise? Mark?”

The voice sounded out of the air close to Louise’s ear. “Yes, Trapper-of-Frogs. I hear you. Where are you?”

“I’m in the forest. I — ”

“Yes?”

“I think you’d better get up here.”

Louise looked at Mark; he was frowning, and no doubt some sub-projection of him was already with Trapper.

“Why?” Louise asked. “What’s wrong. Trapper?”

“Nothing’s wrong. Not exactly. It’s just — different…”