Shawcross broke into a sweat. The sinners next door moaned as if already in Hell, the thin dividing wall vibrated, the wind rose up to shake the dark trees and rattle his window. What was this wild idea in his head? A true message from God, or the product of his own imperfect understanding? He needed guidance! He switched on his reading lamp and picked up his Bible from the bedside table. With his eyes closed, he opened the book at random.

 He recognised the passage at the very first glance. He ought to have; he'd read it and reread it a hundred times, and knew it almost by heart. The destruction of Sodom and Gomorrah.

 At first, he tried to deny his destiny: He was unworthy! A sinner himself! An ignorant child! But everyone was unworthy, everyone was a sinner, everyone was an ignorant child in God's eyes. It was pride, not humility, that spoke against God's choice of him.

 By morning, not a trace of doubt remained.

 Dropping paleontology was a great relief; defending Creationism with any conviction required a certain, very special, way of thinking, and he had never been quite sure that he could master it. Biochemistry, on the other hand, he mastered with ease (confirmation, if any was needed, that he'd made the right decision). He topped his classes every year, and went on to do a PhD in Molecular Biology at Harvard, then postdoctoral work at the NIH, and fellowships in Canada and France. He lived for his work, pushing himself mercilessly, but always taking care not to be too conspicuous in his achievements. He published very little, usually as a modest third or fourth co-author, and when at last he flew home from France, nobody in his field knew, or would have much cared, that John Shawcross had returned, ready to begin his real work.

 Shawcross worked alone in the gleaming white building that served as both laboratory and home. He couldn't risk taking on employees, no matter how closely their beliefs might have matched his own. He hadn't even let his parents in on the secret; he told them he was engaged in theoretical molecular genetics, which was a lie of omission only - and he had no need to beg his father for money week by week since, for tax reasons, twenty-five percent of the Shawcross empire's massive profit was routinely payed into accounts in his name.

 His lab was filled with shiny grey boxes, from which ribbon cables snaked to PCs; the latest generation, fully automated, synthesisers and sequencers of DNA, RNA, and proteins (all available off the shelf, to anyone with the money to buy them). Half a dozen robot arms did all the grunt work: pipetting and diluting reagents, labelling tubes, loading and unloading centrifuges.

 At first Shawcross spent most of his time working with computers, searching databases for the sequence and structure information that would provide him with starting points, later buying time on a supercomputer to predict the shapes and interactions of molecules as yet unknown.

 When aqueous X-ray diffraction become possible, his work sped up by a factor of ten; to synthesise and observe the actual proteins and nucleic acids was now both faster, and more reliable, than the hideously complex process (even with the best short-cuts, approximations and tricks) of solving Schrödinger's equation for a molecule consisting of hundreds of thousands of atoms.

 Base by base, gene by gene, the Shawcross virus grew.

As the woman removed the last of her clothes, Shawcross, sitting naked on the motel room's plastic bucket chair, said, "You must have had sexual intercourse with hundreds of men."

 "Thousands. Don't you want to come closer, honey? Can you see okay from there?"

 "I can see fine."

 She lay back, still for a moment with her hands cupping her breasts, then she closed her eyes and began to slide her palms across her torso.

 This was the two hundredth occasion on which Shawcross had paid a woman to tempt him. When he had begun the desensitising process five years before, he had found it almost unbearable. Tonight he knew he would sit calmly and watch the woman achieve, or skilfully imitate, orgasm, without experiencing even a flicker of lust himself.

 "You take precautions, I suppose."

 She smiled, but kept her eyes closed. "Damn right I do. If a man won't wear a condom, he can take his business elsewhere. And I put it on, he doesn't do it himself. When I put it on, it stays on. Why, have you changed your mind?"

 "No. Just curious."

 Shawcross always paid in full, in advance, for the act he did not perform, and always explained to the woman, very clearly at the start, that at any time he might weaken, he might make the decision to rise from the chair and join her. No mere circumstantial impediment could take any credit for his inaction; nothing but his own free will stood between him and mortal sin.

 Tonight, he wondered why he continued. The "temptation" had become a formal ritual, with no doubt whatsoever as to the outcome.

 No doubt? Surely that was pride speaking, his wiliest and most persistent enemy. Every man and woman forever trod the edge of a precipice over the inferno, at risk more than ever of falling to those hungry flames when he or she least believed it possible.

 Shawcross stood and walked over to the woman. Without hesitation, he placed one hand on her ankle. She opened her eyes and sat up, regarding him with amusement, then took hold of his wrist and began to drag his hand along her leg, pressing it hard against the warm, smooth skin.

 Just above the knee, he began to panic - but it wasn't until his fingers struck moisture that he pulled free with a strangled mewling sound, and staggered back to the chair, breathless and shaking.

 That was more like it.

The Shawcross virus was to be a masterful piece of biological clockwork (the likes of which William Paley could never have imagined - and which no godless evolutionist would dare attribute to the "blind watchmaker" of chance). Its single strand of RNA would describe, not one, but four potential organisms.

 Shawcross virus A, SVA, the "anonymous" form, would be highly infectious, but utterly benign. It would reproduce within a variety of host cells in the skin and mucous membranes, without causing the least disruption to normal cellular functions. Its protein coat had been designed so that every exposed site mimicked some portion of a naturally occurring human protein; the immune system, being necessarily blind to these substances (to avoid attacking the body itself), would be equally blind to the invader.

 Small numbers of SVA would make their way into the blood stream, infecting T-lymphocytes, and triggering stage two of the virus's genetic program. A system of enzymes would make RNA copies of hundreds of genes from every chromosome of the host cell's DNA, and these copies would then be incorporated into the virus itself. So, the next generation of the virus would carry with it, in effect, a genetic fingerprint of the host in which it had come into being.

 Shawcross called this second form SVC, the C standing for "customised" (since every individual's unique genetic profile would give rise to a unique strain of SVC), or "celibate" (because, in a celibate person, only SVA and SVC would be present).

 SVC would be able to survive only in blood, semen and vaginal fluids. Like SVA, it would be immunologically invisible, but with an added twist: its choice of camouflage would vary wildly from person to person, so that even if its disguise was imperfect, and antibodies to a dozen (or a hundred, or a thousand) particular strains could be produced, universal vaccination would remain impossible.

 Like SVA, it would not alter the function of its hosts - with one minor exception. When infecting cells in the vaginal mucous membrane, the prostate, or the seminiferous epithelium, it would cause the manufacture and secretion from these cells of several dozen enzymes specifically designed to degrade varieties of rubber. The holes created by a brief exposure would be invisibly small - but from a viral point of view, they'd be enormous.