It was massive. It had caused a well in spacetime so deep that it was drawing in galaxies, including Earth’s Milky Way, from across hundreds of millions of light-years.

"I don’t believe it." Parz said, shaking in sympathy with the Spline.

"It is an artifact," the Qax said. "A Xeelee construct. Bolder watched the Xeelee build it."

Xeelee craft — cup-shaped freighters the size of moons, and fighters with night-dark discontinuity wings hundreds of miles wide — patrolled the huge construction site. With cherry-red starbreaker beams they smashed the infalling, blue-shifted galactic fragments; they plated layers over the growing Ring.

"We believe the Xeelee have already invested billions of years in this project," the Qax said. "But its growth is exponential. The more massive it becomes, the deeper the gravity well grows, and the faster matter falls toward the site, feeding the construction crews further."

"But why? What’s the point of it?"

"We speculate that the Xeelee are trying to construct a Kerr metric region," the Qax said.

"A what?"

The Kerr metric was a human description for a special solution of Einstein’s equations of general relativity. When spacetime was distorted by a sufficiently massive, rotating toroid, it could — open.

"Like a wormhole?" Parz asked.

"Yes. But the Kerr metric interface would not connect two points in the same spacetime, Parz. It is a throat between spacetimes."

Parz struggled to understand that. "You’re saying that the artifact is a doorway — a way out of our universe?"

"Crudely, yes. The Xeelee are trying to build an exit from this cosmos."

"And to do it they’re prepared to wreck a region of space hundreds of millions of lightyears wide…"

Suddenly Parz was blind again. Hurriedly, panicking, he snapped subvocal commands; but this time his vision would not clear. The darkness in which he was immersed was deeper than the inside of his own eyelids… it was, he realized with a terrifying clarity, the darkness of nothingness, of emptiness. "Qax." His own voice was muffled; it was as if all his senses were failing together. "What’s happening to me?"

The Qax’s voice came to him, distant but clear. "This is causality stress, Parz. The severance of the causal lines, of the quantum wave functions in which you are embedded. Causality stress is causing sensory dysfunction—"

Jasoft felt his body sense softening, drifting away from him; he felt as if he were becoming disembodied, a mote of consciousness without anchor in the external universe.

The Qax continued to speak. Its words were like distant trumpet notes. "Jasoft Parz. This is as difficult for me, for any sentient being, as it is for you… even for the Spline. But it will pass. Do not let it undermine your sanity. Concentrate on what I am saying to you.

"Jim Bolder, in his stolen craft, evaded the Xeelee engineers. He returned to the Qax home system, where his journey had begun. Jasoft, the Qax are a trading nation. Bolder had returned with a treasure valuable beyond price: data on the greatest Xeelee artifact. It will not surprise you that the Qax decided to, ah, retain the data.

"But Bolder tricked us."

There was a glimmering around Parz now, a ghostly shimmer, a reflection of ripples, like moonlight on a sea.

"The details have never become clear. Bolder should have emerged from hyperspace into a region surrounded by Spline warships, all bearing gravity-wave starbreaker technology… He failed to do so. Bolder survived, escaped.

"Starbreakers were used. In the confusion and panic, they brushed the Qax sun. It was enough to cause the sun to become unstable — ultimately, to nova.

"The Qax were forced to flee. Dozens of individuals died in the exodus. Our power was lost, and the Occupation of Earth crumbled…"

Jasoft Parz, bewildered and disoriented as he was, could not help but exult at this.

A gray light, without form and structure, spread into existence around him… No, not around him, he realized; he was part of this light: it was as if this were the gray light that shone beneath reality, the light against which all phenomena are shadows. His panic subsided, to be replaced by a sense of calm power; he felt as if he were light-years wide and yet no wider than an atom, a million years old and yet fresher than a child’s first breath.

"Qax. What the hell is happening?"

"Causality stress, Parz. Perceptual dysfunction. Causality is not a simple phenomenon. When objects are once joined, they become part of a single quantum system… and they must remain joined forever thereafter, via superlight quantum effects. You should imagine you are walking across a beach, calling into existence a trail of footsteps as you go. The footsteps may fade with time as you pass on, but each of them remains bound to you by the threads of quantum functions."

"And when I pass out of my own region of spacetime?"

"The threads are cut. Causal bonds are broken and must be re-formed…"

"Dear God, Qax. Is this pain worth it, just to travel through time?"

"To achieve one’s goals: yes," the Qax said quietly.

"Finish the story," Jasoft Parz said.

"Finish it?"

"Why are the Xeelee building a way out of the universe? What are they seeking?"

"I suspect if we knew the answer to that," the Qax said, "we would know much of the secret truth of our universe. But we do not. The story must remain unfinished, Jasoft Parz.

"But consider this. What if the Xeelee are not seeking something beyond their Ring — but are fleeing something in this universe?

"What do Xeelee fear, do you suppose?"

Parz, buffeted, disoriented, could find no reply.

The Spline warship surged through time.

The Friend of Wigner, Jaar, was waiting for Michael Poole at the entrance to the Crab’s grounded boat.

Poole stood on the boat’s exit ramp, bathed in eerie Jovian light. He looked out at the waiting young man, the scatter of Xeelee construction-material buildings in the distance, the glimpses of ancient stones — and over it all the looming, perfect curve of Jupiter.

He felt too old for this.

He’d got through the events of the previous day — the landing, the encounter with Miriam, the bombardment of strangeness — on a kind of psychic momentum. But the momentum had gone now; he’d emerged only reluctantly from a troubled sleep to face the dangers, the pressures of the day, the need to find a way to deal with Miriam’s presence here.

Miriam had spent the sleeping period in the boat. Harry had had the decency to abandon his rights-for-AIs rhetoric for a few hours and had gone into stasis to leave them alone. But Miriam and Michael hadn’t slept together. What were they, kids? They had talked, and held each other’s hands, and finally stumbled to separate bunks. Somehow an acquiescence to lust didn’t seem the right reaction to a century of separation, the renewal of an antique, and combative, relationship.

He wished he hadn’t let Harry talk him into this jaunt. He would have exchanged all he had seen and learned to return to the calmness of his station in the Oort Cloud, his slow tinkering at the fringes of exotic-matter physics.

Of course if he got his head cleaned out, as Harry had done, he’d be able to face all this with a fresh eye.

Well, the hell with that.

Poole walked down the ramp and onto the tough English grass. The Wigner’s Friend smiled at him; Poole saw a young man, tall and whiplash thin, dressed in the standard-issue pink coverall. Bony wrists and ankles protruded from the coarse material. Under a high, cleanshaven dome of a scalp he shared the pallid, hothouse complexion of Shira, and his eyes were watery-brown. Jaar’s stance was a little awkward. Poole guessed that even fifteen centuries hence someone of this height and build would spend his life ducking to avoid looking clumsy, but there was something beyond that, something about the way the Friend’s legs looked bowed -