BOXING DAY

7 PM

LONDON was cold. No snow had fallen here, but a freezing wind whipped the ancient buildings and the curled streets, and people hunched their shoulders and tightened the scarves around their necks as they hurried to the warmth of pubs and restaurants, hotels and cinemas.

Toni Gallo sat in the back of a plain gray Audi beside Odette Cressy. Odette was a blond woman Toni's age, wearing a dark business suit over a scarlet shirt. Two detectives sat in the front, one driving, one studying a direction-finding radio receiver and telling the driver where to go.

The police had been tracking the perfume bottle for thirty-three hours. The helicopter had landed, as expected, in southwest London. The pilot had got into a waiting car and driven across Battersea Bridge to the riverside home of Adam Hallan. All last night the radio transmitter had remained stationary, beeping steadily from somewhere in the elegant eighteenth-century house. Odette did not want to arrest Hallan yet. She wanted to catch the maximum number of terrorists in her net.

Toni had spent most of that time asleep. When she lay down in her flat just before noon on Christmas Day, she felt too tense to sleep. Her thoughts were with the helicopter as it flew the length of Britain, and she worried that the tiny radio beacon would fail. Despite her anxieties, she had dropped off in seconds.

In the evening, she had driven to Steepfall to see Stanley. They had held hands and talked for an hour in his study, then she flew to London. She slept heavily all night at Odette's flat in Camden Town.

As well as following the radio signal, the Metropolitan Police had Adam Hallan and his pilot and copilot under surveillance. In the morning Toni and Odette joined the team watching Adam Hallan's house.

Toni had achieved her main objective. The deadly virus samples were back in the BSL4 laboratory at the Kremlin. But she also hoped to catch the people responsible for the nightmare she had lived through. She wanted justice.

Today Hallan had given a lunch party, and fifty people of assorted nationalities and ages, all wearing expensive casual clothes, had visited the house. One of the guests had left with the perfume bottle. Toni and Odette and the team tracked the radio beacon to Bayswater and kept watch over a student rooming house all afternoon.

At seven o'clock in the evening, the signal moved again.

A young woman came out of the house. In the light of the street lamps, Toni could see that she had beautiful dark hair, heavy and lustrous. She carried a shoulder bag. She turned up the collar of her coat and walked along the pavement. A detective in jeans and an anorak got out of a tan Rover and followed her.

"I think this is it," Toni said. "She's going to release the spray."

"I want to see it," Odette said. "For the prosecution, I need witnesses to the attempted murder."

Toni and Odette lost sight of the young woman as she turned into a Tube station. The radio signal weakened worryingly as the woman went underground. It remained steady for a while, then the beacon moved, presumably because the woman was on a train. They followed the feeble signal, fearing it would fade out and she would shake off the detective in the anorak. But she emerged at Piccadilly Circus, the detective still tailing her. They lost visual contact for a minute when she turned into a one-way street, then the detective called Odette on his mobile phone and reported that the woman had entered a theater.

Toni said, "That's where she'll release the spray."

The unmarked police cars drew up outside the theater. Odette and Toni went in, followed by two men from the second car. The show, a ghost story with songs, was popular with visiting Americans. The girl with beautiful hair was standing in the queue for collection of prepaid tickets.

While she waited, she took from her shoulder bag a perfume bottle. With a quick gesture that looked entirely natural, she sprayed her head and shoul............