"Be ready."

Now the plane passed over Poole’s head and away from him. For a few seconds there was a disconcerting feeling of falling upward that rapidly translated, as Poole’s sensorium went through a hundred-eighty-degree swivel, to a sense of plummeting headfirst downward. Then came rotation, the sharp pull of Coriolis forces at his belly. The elevator cage was turning about an axis somewhere near his waist. Oddly enough Poole did not feel threatened now; it was like being a small child again, like swinging through the air in the strong, safe arms of Harry. The real Harry.

The turn was completed. The sideways Coriolis died away; with a sigh of relief Poole felt himself settle to a normal-feeling floor. Not quite normal; he felt his ears pop. Jaar smiled kindly at him. "Don’t worry," he said. "It took me a while to get used to it."

Poole frowned, feeling an absurd need to demonstrate his manhood to this young man. "I’ve told you, you don’t need to coddle me. We’ve passed through the plane; now we’ve turned upside down, so the holes are beneath our feet again, and everything feels normal. Right?"

Jaar nodded, in unmoved assent. He palmed another section of the wall and the elevator door panel slid aside.

Jaar stepped out onto a clear, glassy surface. Poole followed, almost stumbling; in the gentle gravity the clear surface was as slippery as hell. When he was steady on his feet, Poole raised his head.

The earth-craft was hollow.

Poole was at the center of an artificial cave that looked as if it occupied most of the craft’s bulk. Above his head there was a dome of Xeelee dove-gray, about twenty yards tall at its highest point, and below him a sheet of glass that met the dome at a seamless horizon. Beneath the glass was a hexagonal array of blue and pink bars, each cell in the array about a yard wide.

Tubes of glass — hollow shafts, each a yard wide — rained from the roof, terminating six feet above the floor. It made the dome look like some huge, absurd chandelier, Poole thought. A blocky control console was fixed to the floor beneath each tube. Through the holes in the roof Poole could see patches of Jovian cloud-pink. The shafts looked like fairy-land cannon, pointing at Jupiter.

People — young men and women in pink jumpsuits, Wigner’s Friends — moved about the clear surface, talking and carrying the ubiquitous AI slates; the huge, sparkling pillars dangled unnoticed above their heads like trapped sunlight. The Friends moved with the mercury-slow grace Poole associated with inhabitants of low-gravity worlds like Luna. Their voices, low and serious, carried clearly to Poole, and it was as if he were inside some huge building — perhaps a travel terminus.

The diffuse light seemed to come from the domed ceiling itself, with a little blue-pink toning from the array beneath the floor. It was like being inside a huge lightbulb. Or, perhaps, in the imaginary caverns inside the Earth conjured up by one of Poole’s favorite authors, the ancient Verne.

Jaar smiled and bowed slightly. "So," he said, "the guided tour. Over your head we have a dome of Xeelee construction material. In fact the construction material passes under the floor we stand on and under the singularity plane, forming a shell within the craft broken only by the access shafts."

"Why?"

Jaar shrugged. "Construction material is impervious to all known radiation."

"So it protects the passengers from riding so close to the black holes."

"And it prevented the Qax from detecting our activity and becoming overly suspicious. Yes. In addition, our hyperdrive engine has been incorporated into the fabric of the construction-material shell."

"How did you build the Xeelee shell?"

Jaar rubbed his nose. "You don’t ‘build’ construction material. You grow it. It took humans centuries to work out how, from the first discovery of abandoned Xeelee flowers."

Poole pointed to the floor. "And under here, the plane of singularities."

Jaar dropped to one knee; Poole joined him, and they peered through the floor at the enigmatic spokes of blue and pink-violet. Jaar said, "This surface is not a simple transparent sheet; it is semisentient. What you see here is largely a false-color rendering.

"You have deduced, from your observations of the dimpled gravity field on the surface, that our craft is held together by mini-black hole singularities." He pointed to a node in the hexagonal array. "There is one of them. We manufactured and brought about a thousand of the holes with us through time, Michael."

The holes, the Friend explained, were charged, and were held in place by an electromagnetic lattice. The false colors showed plasma flux lines in the lattice, and high-frequency radiation from infalling matter crushed by the singularities.

Hawking evaporation caused each singularity to glow at a temperature measured in teradegrees. The megawatts generated by the captive, evaporating holes provided the earth-craft’s power — power for the hyperdrive, for example.

The evaporation was whittling away at the mass-energy of each hole, inexorably. But it would take a billion years for the holes to evaporate completely.

Poole peered at the gaudy display somberly; it was difficult to believe that only a few feet beneath him was an object smaller than an electron but with the mass of a city block, a pinpoint flaw in the structure of spacetime itself. And below that was a plane of grass from which clung, like flies to a ceiling, the Crab’s boat; Berg, Shira, and the rest; the toylike buildings of the Friends of Wigner; and — oddest of all — the ancient stones of the henge, dangling there in Jupiter’s light like a rocky chandelier — or perhaps like rotting teeth in the upper jaw of an incomplete, furred-over skull.

There must be a layer of air all the way around this craft, he thought. Of course the air must get pretty thin away from the high-gravity regions, close to the center of the plane of singularities.

Stiffly, he climbed to his feet. "I’m grateful for what you’ve shown me," he said.

Jaar studied him, tall, very bald, disturbingly pale. "And what do you feel you have learned?"

Poole shrugged, deliberately casual. With a wave of his hand he indicated the cavern. "Nothing new. All this is impressive, but it’s just detail. The singularity array. There is the meat of the mission; there’s what you’ve gone to all this trouble to bring back through time." He pointed to the shafts that led to the rents in the construction-material dome. "Those things look like cannon barrels, pointing at Jupiter. I think they are cannon — singularity cannons. I think that one by one you’re going to release these singularities from their electromagnetic nets and propel them out of those tubes and toward Jupiter."

Jaar nodded slowly. "And then what will we do?"

Poole spread his hands. "Simply wait…"

He pictured a singularity — a tiny, all but invisible, fierce little knot of gamma radiation — swooping in great, slow ellipses around Jupiter, on each orbit blasting a narrow channel through the thin gases at the roof of the atmosphere. There would be a great deal of drag; plasma bow waves would haul at the singularity as it plunged through the air.

Eventually, like grasping hands, the atmosphere would claim the singularity.

Rapidly spiraling inward, the hole would scythe through Jupiter’s layers of methane and hydrogen, at last plunging into the core of metallic hydrogen. It would come to rest, somewhere close to Jupiter’s gravitational center. And it would start to grow.

"You’ll send in more and more," Poole said. "Soon there will be a swarm of singularities, orbiting each other like insects inside the solid heart of the planet. And all growing inexorably, absorbing more and more of Jupiter’s substance. Eventually some of the holes will collide and merge, I guess, sending out gravitational waves that will disrupt the outer layers of the planet even more." Maybe, Poole speculated, the Friends could even control the merging of the holes — direct the pulsed gravity waves to sculpt the collapse of the planet.