The chip in the card contained details of his father's fingerprint. It was not a simple image, for that was too easy to fake-a photograph of the finger could fool a normal scanner. Rather, Kit had built a device that measured twenty-five points of the fingerprint, using minute electrical differences between ridges and valleys. He had also written a program that stored these details in code. At his apartment he had several prototypes of the fingerprint scanner and he had, naturally, kept a copy of the software he had created.

Now he set his laptop to read the smart card. The only danger was that someone at Oxenford Medical-Toni Gallo, perhaps-might have modified the software so that Kit's program would no longer work; for example, by requiring an access code before the card could be read. It was unlikely that anyone would have gone to such trouble and expense to guard against a possibility that must have seemed fanciful-but it was conceivable. And he had not told Nigel about this potential snag.

He waited a few anxious seconds, watching the screen.

At last it shimmered and displayed a page of code: Stanley's fingerprint details. Kit sighed with relief and saved the file.

His niece Caroline walked in, carrying a rat.

She was dressed younger than her age, in a flower-patterned dress and white stockings. The rat had white fur and pink eyes. Caroline sat on the sleepchair, stroking her pet.

Kit suppressed a curse. He could hardly tell her that he was doing something secret and would prefer to be alone. But he could not continue while she sat there.

She had always been a nuisance. From an early age she had hero-worshipped her young Uncle Kit. As a boy he had quickly wearied of this and become fed up with the way she followed him around. But she was hard to shake off.

He tried to be nice. "How's the rat?" he said.

"His name is Leonard," she replied in a tone of mild reproof.

"Leonard. Where did you get him?"

"Paradise Pets in Sauchiehall Street." She let the rat go, and it ran up her arm and perched on her shoulder.

Kit thought the girl was insane, carrying a rat around as if it were a baby. Caroline looked like her mother, Olga, with long dark hair and heavy black eyebrows, but where Olga was dryly severe, Caroline was as wet as a rainy February. She was only seventeen, she might grow out of it.

He hoped she was too wrapped up in herself and her pet to notice the card sticking up out of the reader and the words "Oxenford Medical" printed along its top. Even she would realize he was not supposed to have a pass for the Kremlin nine months after he was fired.

"What are you doing?" she asked him.

"Work. I need to finish this today." He longed to snatch the telltale card out of the reader, but he feared that would only call her attention to it.

"I won't bother you, just carry on."

"Nothing happening downstairs?"

"Mummy and Aunt Miranda are stuffing the stockings in the drawing room, so I've been chucked out."

"Ah." He turned back to the computer and switched the software into "Read" mode. His next step should be to scan his own fingerprint, but he could not let her see that. She might not grasp the significance herself, but she could easily mention it to someone who would. He pretended to study the screen, racking his brains for a way to get rid of her. After a minute he was inspired. He faked a sneeze.

"Bless you," she said.

"Thanks." He sneezed again. "You know, I think poor dear Leonard is doing this to me."

"How could he?" she said indignantly.

"I'm slightly allergic, and this room is so small."

She stood up. "We don't want to make people sneeze, do we, Lennie?" She went out.

Kit closed the door gratefully behind her, then sat down and pressed the forefinger of his right hånd to the glass of the scanner. The program scrutinized his fingerprint and encoded the details. Kit saved the file.

Finally, he uploaded his own fingerprint details to the smart card, overwriting his father's. No one else could have done this, unless they had copies of Kit's own software, plus a stolen smart card with the correct site code. If he were devising the system anew he still would not bother to make the cards nonrewritable. Nevertheless, Toni Gallo might have. He looked anxiously at the screen, half-expecting an error message saying "YOU DO NOT HAVE ACCESS."

No such message appeared. Toni had not outsmarted him this time. He reread the data from the chip, to make sure the procedure had been successful. It had: the card now carried Kit's fingerprint details, not Stanley's. "Yes!" he said aloud, mutedly triumphant.

He removed the card from the machine and put it in his pocket. It would now give him access to BSL4. When he waved the card at the reader, and pressed his finger to the touch screen, the computer would read the data on the card and compare it with the fingerprint, find they matched, and unlock the door.

After he returned from the lab, he would reverse the process, erasing his own fingerprint data from the chip and reinstating Stanley's, before he replaced the card in his father's wallet sometime tomorrow. The computer at the Kremlin would record that Stanley Oxenford had entered BSL4 in the early hours of 25 December. Stanley would protest that he had been at home in bed, and Toni Gallo would tell the police that no one else could have used Stanley's card because of the fingerprint check. "Sweet," he said aloud. It pleased him to think how baffled they would all be.

Some biometric security systems matched the fingerprint with data stored on a central computer. If the Kremlin had used that configuration, Kit would have needed access to the database. But employees had an irrational aversion to the thought of their personal details being stored on company computers. Scientists in particular often read the Guardian and became finicky about their civil rights. Kit had chosen to store the fingerprint record on the smart card, rather than the central database, to make the new security setup more acceptable to the staff. He had not anticipated that one day he would be trying to defeat his own scheme.

He felt satisfied. Stage One was complete. He had a working pass for BSL4. But, before he could use it, he had to get inside the Kremlin.

He took his phone from his pocket. The number he dialed was the mobile of Hamish McKinnon, one of the security guards on duty at the Kremlin tonight. Hamish was the company dope dealer, supplying marijuana to the younger scientists and Ecstasy to the secretaries for their weekends. He did not deal in heroin or crack, knowing that a serious addict was sure to betray him sooner or later. Kit had asked Hamish to be his inside man tonight, confident that Hamish would not dare to spill the beans, having his own secrets to conceal.

"It's me," Kit said when Hamish answered. "Can you talk?"

"And a happy Christmas to you too, Ian, you old bugger," Hamish said cheerily. "Just a tick, I'm going to step outside… That's better."

"Everything all right?"

Hamish's voice became serious. "Aye, but she's doubled the guard, so I've got Willie Crawford with me."

"Where are you stationed?"

"In the gatehouse."

"Perfect. Is everything quiet?"

"Like a graveyard."

"How many guards in total?"

"Six. Two here, two at reception, and two in the control room."

"Okay. We can cope with that. Let me know if anything unusual happens."

"Okay."

Kit ended the call and dialed a number that gave him access to the telephone system computer at the Kremlin. The number was used by Hibernian Telecom, the company that had installed the phones, for remote diagnosis of faults. Kit had worked closely with Hibernian, because the alarms he had installed used phone lines. He knew the number and the access code. Once again, he had a moment of tension, worrying that the number or the code might have been changed in the nine months since he had left. But they had not.