"Never you mind. Just stay put." He jerked Stoney's arm up behind his back with one hand, while grinding his face into the wall with the other. "You're mine now, you piece of s.h.i.t. No one's going to protect you this time."

Stoney addressed Jack through a mouth squashed against the masonry. "Dith ith Pether Quinth, my own perthonal thpook. I did make a Fauthtian bargain. But with thtrictly temporal-"

"Shut up!" Quint pulled a gun from his jacket and held it to Stoney's head.

Jack said, "Steady on."

"Just how far do your connections go?" Quint screamed. "I've had memos disappear, sources clam up-and now my superiors are treating me like some kind of traitor! Well, don't worry: when I'm through with you, I'll have the names of the entire network." He turned to address Jack again. "And don't you think you're going anywhere."

Stoney said, "Leave him out of dith. He'th at Magdalene. You mutht know by now: all the thpieth are at Trinity."

Jack was shaken by the sight of Quint waving his gun around, but the implications of this drama came as something of a relief. Stoney's ideas must have had their genesis in some secret war-time research project. He hadn't made a deal with the devil after all, but he'd broken the Official Secrets Act, and now he was paying the price.

Stoney flexed his body and knocked Quint backward. Quint staggered, but didn't fall; he raised his arm menacingly, but there was no gun in his hand. Jack looked around to see where it had fallen, but he couldn't spot it anywhere. Stoney landed a kick squarely in Quint's t.e.s.t.i.c.l.es; barefoot, but Quint wailed with pain. A second kick sent him sprawling.

Stoney called out, "Luke? Luke! Would you come and give me a hand?"

A solidly built man with tattooed forearms emerged from Stoney's bedroom, yawning and tugging his braces into place. At the sight of Quint, he groaned. "Not again!"

Stoney said, "I'm sorry."

Luke shrugged stoically. The two of them managed to grab hold of Quint, then they dragged him struggling out the door. Jack waited a few seconds, then searched the floor for the gun. But it wasn't anywhere in sight, and it hadn't slid under the furniture; none of the crevices where it might have ended up were so dark that it would have been lost in shadow. It was not in the room at all.

Jack went to the window and watched the three men cross the courtyard, half expecting to witness an a.s.sa.s.sination. But Stoney and his lover merely lifted Quint into the air between them, and tossed him into a shallow, rather slimy-looking pond.

Jack spent the ensuing days in a state of turmoil. He wasn't ready to confide in anyone until he could frame his suspicions clearly, and the events in Stoney's rooms were difficult to interpret unambiguously.

He couldn't state with absolute certainty that Quint's gun had vanished before his eyes. But surely the fact that Stoney was walking free proved that he was receiving supernatural protection? And Quint himself, confused and demoralised, had certainly had the appearance of a man who'd been demonicallyconfounded at every turn.

If this was true, though, Stoney must have bought more with his soul than immunity from worldly authority. The knowledge itself had to be Satanic in origin, as the legend of Faustus described it. Tollers had been right, in his great essay "Mythopoesis": myths were remnants of man's pre-lapsarian capacity to apprehend, directly, the great truths of the world. Why else would they resonate in the imagination, and survive from generation to generation?

By Friday, a sense of urgency gripped him. He couldn't take his confusion back to Potter's Barn, back to Joyce and the boys. This had to be resolved, if only in his own mind, before he returned to his family.

With Wagner on the gramophone, he sat and meditated on the challenge he was facing. Stoney had to be thwarted, but how? Jack had always said that the Church of England-apparently so quaint and harmless, a Church of cake stalls and kindly spinsters-was like a fearsome army in the eyes of Satan.

But even if his master was quaking in h.e.l.l, it would take more than a few stern words from a bicycling vicar to force Stoney to abandon his obscene plans.

But Stoney's intentions, in themselves, didn't matter. He'd been granted the power to dazzle and seduce, but not to force his will upon the populace. What mattered was how his plans were viewed by others. And the way to stop him was to open people's eyes to the true emptiness of his apparent cornucopia.

The more he thought and prayed about it, the more certain Jack became that he'd discerned the task required of him. No denunciation from the pulpits would suffice; people wouldn't turn down the fruits of Stoney's d.a.m.nation on the mere say-so of the Church. Why would anyone reject such l.u.s.trous gifts, without a carefully reasoned argument?

Jack had been humiliated once, defeated once, trying to expose the barrenness of materialism. But might that not have been a form of preparation? He'd been badly mauled by Ans...o...b.., but she'd made an infinitely gentler enemy than the one he now confronted. He had suffered from her taunts-but what was suffering, if not the chisel G.o.d used to shape his children into their true selves?

His role was clear, now. He would find Stoney's intellectual Achilles heel, and expose it to the world.

He would debate him.

3.

Robert gazed at the blackboard for a full minute, then started laughing with delight. "That's so beautiful!"

"Isn't it?" Helen put down the chalk and joined him on the couch. "Any more symmetry, and nothing would happen: the universe would be full of crystalline blankness. Any less, and it would all be uncorrelated noise."

Over the months, in a series of tutorials, Helen had led him through a small part of the century of physics that had separated them at their first meeting, down to the purely algebraic structures that lay beneath s.p.a.cetime and matter. Mathematics catalogued everything that was not self contradictory; within that vast inventory, physics was an island of structures rich enough to contain their own beholders.

Robert sat and mentally reviewed everything he'd learned, trying to apprehend as much as he could in a single image. As he did, a part of him waited fearfully for a sense of disappointment, a sense of anticlimax. He might never see more deeply into the nature of the world. In this direction, at least, there was nothing more to be discovered.

But anticlimax was impossible. To become jaded with this was impossible. However familiar he became with the algebra of the universe, it would never grow less marvelous.

Finally he asked, "Are there other islands?" Not merely other histories, sharing the same underlying basis, but other realities entirely.

"I suspect so," Helen replied. "People have mapped some possibilities. I don't know how that could ever be confirmed, though."

Robert shook his head, sated. "I won't even think about that. I need to come down to Earth for awhile." He stretched his arms and leaned back, still grinning.

Helen said, "Where's Luke today? He usually shows up by now, to drag you out into the sunshine."

The question wiped the smile from Robert's face. "Apparently I make poor company. Being insufficiently fanatical about darts and football."

"He's left you?" Helen reached over and squeezed his hand sympathetically. A little mockingly, too.

Robert was annoyed; she never said anything, but he always felt that she was judging him. "You think I should grow up, don't you? Find someone more like myself. Some kind of soulmate." He'd meant the word to sound sardonic, but it emerged rather differently.

"It's your life," she said.

A year before, that would have been a laughable claim, but it was almost the truth now. There was a de facto moratorium on prosecutions, while the recently acquired genetic and neurological evidence was being a.s.sessed by a parliamentary subcommittee. Robert had helped plant the seeds of the campaign, but he'd played no real part in it; other people had taken up the cause. In a matter of months, it was possible that Quint's cage would be smashed, at least for everyone in Britain.

The prospect filled him with a kind of vertigo. He might have broken the laws at every opportunity, but they had still molded him. The cage might not have left him crippled, but he'd be lying to himself if he denied that he'd been stunted.

He said, "Is that what happened, in your past? I ended up in some lifelong partnership?" As he spoke the words, his mouth went dry, and he was suddenly afraid that the answer would be yes. With Chris.

The life he'd missed out on was a life of happiness with Chris.

"No."

"Then what?" he pleaded. "What did I do? How did I live?" He caught himself, suddenly self-conscious, but added, "You can't blame me for being curious."

Helen said gently, "You don't want to know what you can't change. All of that is part of your own causal past now, as much as it is of mine."

"If it's part of my own history," Robert countered, "don't I deserve to know it? This man wasn't me, but he brought you to me."

Helen considered this. "You accept that he was someone else? Not someone whose actions you're responsible for?"

"Of course."

She said, "There was a trial, in 1952. For 'Gross Indecency contrary to Section 11 of the Criminal Amendment Act of 1885.' He wasn't imprisoned, but the court ordered hormone treatments."

"Hormone treatments?" Robert laughed. "What-testosterone, to make him more of a man?"

"No, estrogen. Which in men reduces the s.e.x drive. There are side-effects, of course.

Gynecomorphism, among other things."

Robert felt physically sick. They'd chemically castrated him, with drugs that had made him sprout b.r.e.a.s.t.s. Of all the bizarre abuse to which he'd been subjected, nothing had been as horrifying as that.

Helen continued, "The treatment lasted six months, and the effects were all temporary. But two years later, he took his own life. It was never clear exactly why."

Robert absorbed this in silence. He didn't want to know anything more.

After a while, he said, "How do you bear it? Knowing that in some branch or other, every possible form of humiliation is being inflicted on someone?"

Helen said, "I don't bear it. I change it. That's why I'm here."

Robert bowed his head. "I know. And I'm grateful that our histories collided. But how many histories don't?" He struggled to find an example, though it was almost too painful to contemplate; since their first conversation, it was a topic he'd deliberately pushed to the back of his mind. "There's not just an unchangeable Auschwitz in each of our pasts, there are an astronomical number of others-along with an astronomical number of things that are even worse."

Helen said bluntly, "That's not true."

"What?" Robert looked up at her, startled.

She walked to the blackboard and erased it. "Auschwitz has happened, for both of us, and no oneI'm aware of has ever prevented it-but that doesn't mean that n.o.body stops it, anywhere." She began sketching a network of fine lines on the blackboard. "You and I are having this conversation in countless microhistories-sequences of events where various different things happen with subatomic particles throughout the universe-but that's irrelevant to us, we can't tell those strands apart, so we might as well treat them all as one history." She pressed the chalk down hard to make a thick streak that covered everything she'd drawn. "The quantum decoherence people call this 'coa.r.s.e graining.' Summing over all these indistinguishable details is what gives rise to cla.s.sical physics in the first place.

"Now, 'the two of us' would have first met in many perceivably different coa.r.s.e-grained histories-and furthermore, you've since diverged by making different choices, and experiencing different external possibilities, after those events." She sketched two intersecting ribbons of coa.r.s.e-grained histories, and then showed each history diverging further.

"World War II and the Holocaust certainly happened in both of our pasts-but that's no proof that the total is so vast that it might as well be infinite. Remember, what stops us successfully intervening is the fact that we're reaching back to a point where some of the parallel interventions start to bite their own tail. So when we fail, it can't be counted twice: it's just confirming what we already know."

Robert protested, "But what about all the versions of '30s Europe that don't happen to lie in either your past or mine? Just because we have no direct evidence for a Holocaust in those branches, that hardly makes it unlikely."

Helen said, "Not unlikely per se, without intervention. But not fixed in stone either. We'll keep trying, refining the technology, until we can reach branches where there's no overlap with our own past in the '30s. And there must be other, separate ribbons of intervention that happen in histories we can never even know about."

Robert was elated. He'd imagined himself clinging to a rock of improbable good fortune in an infinite sea of suffering-struggling to pretend, for the sake of his own sanity, that the rock was all there was. But what lay around him was not inevitably worse; it was merely unknown. In time, he might even play a part in ensuring that every last tragedy was not repeated across billions of worlds.

He reexamined the diagram. "Hang on. Intervention doesn't end divergence, though, does it? You reached us, a year ago, but in at least some of the histories spreading out from that moment, won't we still have suffered all kinds of disasters, and reacted in all kinds of self-defeating ways?"

"Yes," Helen conceded, "but fewer than you might think. If you merely listed every sequence of events that superficially appeared to have a non-zero probability, you'd end up with a staggering catalog of absurdist tragedies. But when you calculate everything more carefully, and take account of Planck-scale effects, it turns out to be nowhere near as bad. There are no coa.r.s.e-grained histories where boulders a.s.semble themselves out of dust and rain from the sky, or everyone in London or Madras goes mad and slaughters their children. Most macroscopic systems end up being quite robust-people included. Across histories, the range of natural disasters, human stupidity, and sheer bad luck isn't overwhelmingly greater than the range you're aware of from this history alone."

Robert laughed. "And that's not bad enough?"

"Oh, it is. But that's the best thing about the form I've taken."

"I'm sorry?"

Helen tipped her head and regarded him with an expression of disappointment. "You know, you're still not as quick on your feet as I'd expected."

Robert's face burned, but then he realized what he'd missed, and his resentment-vanished.

"You don't diverge? Your hardware is designed to end the process? Your environment, your surroundings, will still split you into different histories-but on a coa.r.s.e-grained level, you don't contribute to the process yourself?"

"That's right."

Robert was speechless. Even after a year, she could still toss him a hand grenade like this.

Helen said, "I can't help living in many worlds; that's beyond my control. But I do know that I'm one person. Faced with a choice that puts me on a knife-edge, I know I won't split and take every path."

Robert hugged himself, suddenly cold. "Like I do. Like I have. Like all of us poor creatures of flesh."Helen came and sat beside him. "Even that's not irrevocable. Once you've taken this form-if that's what you choose-you can meet your other selves, reverse some of the scatter. Give some a chance to undo what they've done."

This time, Robert grasped her meaning at once. "Gather myself together? Make myself whole?"

Helen shrugged. "If it's what you want. If you see it that way."

He stared back at her, disoriented. Touching the bedrock of physics was one thing, but this possibility was too much to take in.

Someone knocked on the study door. The two of them exchanged wary glances, but it wasn't Quint, back for more punishment. It was a porter bearing a telegram.

When the man had left, Robert opened the envelope.

"Bad news?" Helen asked.

He shook his head. "Not a death in the family, if that's what you meant. It's from John Hamilton.

He's challenging me to a debate. On the topic 'Can A Machine Think?' "

"What, at some university function?"

"No. On the BBC. Four weeks from tomorrow." He looked up. "Do you think I should do it?"

"Radio or television?"

Robert reread the message. "Television."

Helen smiled. "Definitely. I'll give you some tips."

"On the subject?"

"No! That would be cheating." She eyed him appraisingly. "You can start by throwing out your electric razor. Get rid of the permanent five o'clock shadow."

Robert was hurt. "Some people find that quite attractive."

Helen replied firmly, "Trust me on this."