Louise frowned. “Why?”

Mark turned to her, his face expressionless. “We’re in trouble, Louise. The cops are here.”

Spinner-of-Rope asked, “How do you destroy a loop of cosmic string ten million light-years across?”

It isn’t so difficult… if you have the resources of a universe, and a billion years, to play with, Spinner-of Rope. Poole, perched on the shoulder of the nightfighter, pointed at a hail of infalling galaxies swamping a nearby section of the Ring. If the Ring tangles — if cosmic string self-intersects — it cuts itself, he said. It intercommutes. And a new subloop is formed, budding off the old. And perhaps that subloop, too, will self-intersect, and split into still smaller loops… and so on.

Spinner nodded. “I think I understand. It would be an exponential process, once started. Pretty soon, the Ring would decay into the torus of debris we found will find a hundred thousand years from now…”

Yes. No doubt the motion of the Ring has been designed by the Xeelee so that it does not cut itself. But all one need do is start the process, by disrupting the Ring’s periodic behavior. And that is evidently what the photino birds are endeavoring to do, by hurling galaxies — like thrown rocks at the Ring.

Spinner sniffed. “Seems kind of a crude technique.”

Poole laughed. Baryonic chauvinism, Spinner-of-Rope? Besides, the birds have other mechanisms. I —

“…Spinner. Spinner-of-Rope. Can you hear me?”

Spinner sat bolt upright in her couch and clutched at her helmet. “Lieserl? Is that you?”

“Listen to me. We don’t have much time.”

“Oh, Lieserl, I was beginning to think I’d never — ”

“Spinner! Shut up, damn you, and listen.”

Spinner subsided. She’d never heard Lieserl use a tone like that before.

“Use the waldoes, Spinner. You have to get us out of here. Take us straight up, with the hyperdrive, over the plane of the Ring. Have you got that? Use the longest jump distance you can find. We’ll try to patch subroutines into the waldoes, but — ”

“Lieserl, you’re scaring the pants off me. Can’t you tell me what’s wrong?”

“No time, Spinner. Please. Just do it…”

The Universe darkened.

For a bleak, heart-stopping instant Spinner thought she was going blind. But the telltales on the waldoes still gleamed at her, as brightly as ever.

She looked up. There was something before the ship, occluding the blue-shifted galaxy fragments, hiding the Ring.

She saw night-dark wings, spread to their fullest extent, looming over the Northern.

Nightfighters.

She twisted in her seat. There were hundreds of them — impossibly many, dark lanterns hanging in the sky.

They were Xeelee. The Northern was surrounded.

Spinner screamed, and slammed her fists against the hyperdrive waldo.

The ’fighters moved through electric-blue cosmic string like birds through the branches of a forest. There were so many of them in this era. They were cool and magnificent, their nightdark forms arrayed deep into space all around her. Lieserl stared at the swooping, gliding forms, willing herself to see them more clearly. Had any humans ever been closer to Xeelee than this?

The Xeelee moved in tight formation, like bird-flocks, or schools of fish; they executed sudden changes of direction, their domain wall wings beating, in squads spanning millions of miles — absolutely in unison. Now Lieserl saw how ’fighters should be handled, in contrast to Spinner’s earnest, clumsy work. The nightfighters were sculptures of space-time, with a sleek beauty that made her shiver: this was baryonic technology raised to perfection, to a supreme art, she thought.

She was struck by the contrast between this era and the age of devastation — of victory for the photino birds — to which the Northern had first brought them. Here, the Ring was complete and magnificent, and the Xeelee, in their pomp, filled space. Already, she knew, the final defeat was inevitable, and the Xeelee were, in truth, huddling inside their final redoubt. But still, her heart beat harder inside her as she looked out over this, the supremacy of baryonic life.

The overlapping lengths of string slid down, smoothly, past the lifedome, as the Northern climbed. The nightfighters swooped like starlings through the string, and around the Northern — no, Spinner realized suddenly; the nightfighters were flickering across space.

“They’re using their hyperdrive,” she breathed.

Yes. Poole stared up at the nightfighters, his lined face translucent. And we’re hyperdriving too. You’re pushing it, Spinner; we’ve never tried jumps of this scale, even in test. Do you know how fast you’re traveling? Ten thousand light years with every lump… But even so, the Xeelee are easily keeping pace with us.

Of course they are, Spinner thought. They are Xeelee.

These ’fighters could have stopped the Northern at any time — even destroyed it. But they hadn’t.

Why not?

The ship was rising high above the plane of the Ring. The tangle of string fell away from the foreground, and she could see easily now the million-light-year curve of the structure’s limb. And at the heart of the Ring, the singularity seemed to be unfolding toward her, almost welcoming.

The Xeelee ’fighters rose all around her, like leaves in a storm. They can’t believe we’re a threat. I guess humans never were a threat, in truth. Now, it’s almost as if the Xeelee are escorting us, she thought.

“Lieserl,” she said.

“I hear you, Spinner-of-Rope.”

“Tell me what in Lethe’s name we’re doing.”

“You’re taking us out of the plane of the Ring…”

“And then?”

“Down…” Lieserl hesitated. “Look, Spinner, we’ve got to get away from the Xeelee, before they change their mind about us. And we’ve nowhere else to run, not in all of the Universe.”

“And this is your plan?” Spinner was aware of the hysteria in her own voice; she felt fear spread through her stomach and chest, like a cold fluid. “To fly into a singularity?”

Mark punched his thigh. “I was right, damn it,” he said. “I was right all along.”

The tension was a painful presence, clamped around Louise’s throat. “Damn it, Mark, be specific.”

He turned to her. “About the significance of the radio energy flux. Don’t you see? The photino birds have manufactured this immense cavity, of stars and smashed-up galaxies, to imprison the Ring.” He glanced around the skydome. “Lethe. It must have taken them a billion years, but they’ve done it. They’ve built a huge mirror of star stuff, all around the Ring. It’s a feat of cosmic engineering almost on a par with the construction of the Ring itself.”

“A mirror?”

“The interstellar medium is opaque to the radio energy. So each radio photon gets reflected back into the cavity. The photon orbits the Ring — and on each pass it’s super-radiant amplified, as Lieserl described, and so sucks out a little more energy from the inertial drag of the Ring’s rotation. And then the photon heads out again… but it’s still trapped by the galaxy mirror. Back it goes again, to receive a little more amplification… Do you see? It’s a classic example of positive feedback. The trapped radio modes will grow endlessly, leaching energy from the Ring itself…”

“But the modes can’t grow indefinitely,” Morrow said.

“No,” Mark said. “The process is an inertial bomb, Morrow. All that electromagnetic pressure will build up in the cavity, until it can no longer be contained. And in the end — probably only a few tens of millennia from now — it will blow the cavity apart.”