Michael pointed up at the Interface. "And how long before we’re in the guts of that thing?"

Harry thought for a few seconds. "Six minutes, tops."

"Okay, then. That’s why you should forget about the damn drones. By the time they’ve done their worst it will all be over, one way or the other."

Harry pulled a face. "All right, point taken. But it doesn’t get you out of explaining to me how you’re going to blow up the Interface portal." Harry turned his head up to the blue-glowing portal, and — with an evident surge of processing concentration — he produced blue-violet highlights on his Virtual cheekbones. "I mean, if we simply ram that portal the corpse of this damn ship is going to be cut up like ripe cheese, isn’t it?"

"Right. I doubt if you could do much harm to a structure of exotic matter by smashing it with a lump of conventional material; the density difference would make it as absurd as trying to knock down a building by blowing it a kiss… We’re going to enter the Interface as best we can in this tub—"

"And then what?"

"Harry, do you understand how the hyperdrive works?"

Harry grinned. "Yes and no."

"What’s that supposed to mean?"

"It means that I’ve now merged with the residuum of the Spline’s consciousness. And the operation of the hyperdrive is buried in there somewhere… But it’s like working the muscles that let you stand up and walk about. Do you understand me?" He looked at Michael, almost wistfully, his face more boyish than ever. "The Spline core of me knows all about the hyperdrive. But the human shell of Harry, what’s left of it, knows damn-all. And — I find I’m scared, Michael."

Michael found himself frowning, disturbed by Harry’s tone. "You sound — I don’t know — pathetic, Harry."

"Well, I’m sorry you don’t approve," Harry said defiantly. "But it’s honest. I’m still human, son."

Michael shook his head, impatient with the sudden jumble of emotions he found stirring inside him. "The hyperdrive," he said sternly. "All right, Harry. How many dimensions does spacetime have?"

Harry opened his mouth, closed it again. "Four. Three space, one time. Doesn’t it? All wrapped up into some kind of four-dimensional sphere—"

"Wrong. Sorry, Harry. There are actually eleven. And the extra seven is what allows the hyperdrive to work…"

The grand unified theories of physics — the frameworks that merged gravitation and quantum mechanics — predicted that spacetime ought to assume a full eleven dimensions. The logic, the symmetry of the ideas, would allow little else.

And eleven dimensions there turned out to be.

But human senses could perceive only four of those dimensions, directly. The others existed, but on tiny scales. The seven compactified dimensions were rolled into the topological equivalent of tight tubes, with diameters well within the Planck length, the quantum limit to measurement of size.

"Well, so what? Can we observe these compactified tubes?"

"Again, not directly. But, Harry, looked at another way, the tubes determine the values of the fundamental physical constants of the universe. The gravitational constant, the charge on the electron, Planck’s constant — the uncertainty scale—"

Harry nodded. "And if one of these tubes of compactification were opened up a little—"

" — the constants would change. Or," said Michael significantly, "vice versa."

"You’re getting to how the hyperdrive works."

"Yes… As far as I can make out, the hyperdrive suppresses, locally, one of the constants of physics. Or, more likely, a dimensionless combination of them."

"And by suppressing those constants—"

" — you can relax the compactification of the extra dimensions, locally, at least. And by allowing the ship to move a short distance in a fifth spacetime dimension, you can allow it to traverse great distances in the conventional dimensions."

Harry held up his hands. "Enough. I understand how the hyperdrive works. Now tell me what it all means."

Michael turned to him and grinned. "Okay, here’s the plan. We enter the Interface, travel into the wormhole—"

Harry winced. "Let me guess. And then we start up the hyperdrive."

Michael nodded.

The Interface portal was immense over them, now; one glimmering pool of a facet filled Michael’s vision, so close that he could no longer make out the electric blue struts of exotic matter that bounded it.

"Three minutes away," Harry said quietly.

"Okay." As an afterthought Michael added: "Thanks, Harry."

"Michael — I know this won’t, and mustn’t, make a damn bit of difference — but I don’t think there’s any way I can survive this. I can’t function independently of the Spline anymore; I’ve interwoven the AI functionalities of Spline and Crab so much that if one fails, so must the other…"

Michael found himself reaching out to the Virtual of his father; embarrassed, he drew his hand back. "No. I know. I’m sorry, I guess. If it’s any consolation I’m not going to live through it either."

Harry’s young face broke up into a swarm of pixels. "That’s no consolation at all, damn you," he whispered distantly.

The Interface was very close now; Michael caught fugitive reflections of the Spline in that great, glimmering face, as if the facet were some immense pool into which the warship was about to plunge.

Harry crumbled into pixel dust, re-formed again, edgily. "Damn those drones," he grumbled. "Look, Michael, while there’s enough time there’s something I have to tell you—"

The intrasystem freighter settled over the battered, gouged-out Spline eyeball. Cargo bay doors hung open like welcoming lips, revealing a brightly lit hold.

The eye bumped against the hold’s flat ceiling, rebounding softly; a few yards of chewed-up optic nerve followed it like a grizzled umbilical remnant, wrapping itself slowly around the turning eye. Then the hold doors slid shut, and the eye was swallowed.

In an airlock outside the hold, Miriam Berg pressed her face to a thick inspection window. She cradled a heavy-duty industrial-strength hand laser, and her fingers rattled against the laser’s casing as the hold’s pressure equalized.

She cast her eyes around the scuffed walls of the hold with some distaste. This was the Narlikar out of Ganymede, an inter-moon freighter run by a tinpot two-man shipping line. She knew she shouldn’t expect too much of a ship like this. The D’Arcy brothers performed a dirty, dangerous job. Normally this hold would contain water ice from Ganymede or Europa, or exotic sulfur compounds excavated with extreme peril from the stinking surface of Io. So that would explain some of the stains. But sulfur compounds didn’t scratch tasteless graffiti onto the hold walls, she thought. Nor leave sticky patches and half-eaten meals all over — it seemed — every work surface. Still, she was lucky there had been even one ship in the area with the capacity to come and pick up this damn eyeball so quickly. Most of the ships in the vicinity of the Interface portal were clean-lined government or military boats — but it had been the D’Arcy brothers, in their battered old tub, who had come shouldering through the crowd to pick her up from the earth-craft in answer to the frantic, all-channel request she’d put out when she’d realized what Poole was up to.

She watched the Spline eyeball bounce around in the hold’s thickening air. It was like some absurd beachball, she thought sourly, plastered with dried blood and the stumps of severed muscles. But there was a clear area — the lens? — through which human figures, tantalizing obscure, could be seen.

Michael…

Now a synthesized bell chimed softly, and the door separating her from the hold fell open. Towing the laser, Berg threw herself into the eyeball-crowded hold.