Murder, she felt fairly sure, was not the kind of "Purpose of Visit" calculated to speed her through the notoriously difficult U.S. immigration channels. "Pleasure," she ticked, deciding it might not be entirely a lie. At least no one would suspect the truth that lay behind the occupational description of "systems consultant." In spite of the books and films that indicated otherwise, hers was not a job people expected to be carried out by a woman.

She finished filling in the form and looked out of the windows of the jumbo jet. They had chased the sunset west across the Atlantic, and now it was firmly dark blue night out there. Street lights formed a glittering web when they passed above small towns. Over bigger cities, the lights seemed to be enclosed beneath a dimly glowing bowl that held them trapped, the highway lights leading away from them like chains of refugees. Somewhere out there, her target. Watching TV, eating dinner, reading a book, talking to her lover, gossiping on the phone, composing e-mail. Whatever it was, she wouldn't be doing it tomorrow. Not if the woman was successful in her mission.

She turned away from the window and pulled her paperback novel out of the seat pocket. She opened it where she had carefully dog-eared a page to mark her place and carried on reading Northanger Abbey.

A change in engine note signalled the start of the descent into San Francisco. It was a sign she noted with relief. A transatlantic, transcontinental flight was quite long enough for her body to feel permanently realigned into the shape of the aircraft seat. That might be just about bearable in first class, but back in anonymous economy it provoked the irresistible fear that she might never walk properly again. The woman stretched her spine, thrusting shoulders back and chest out. The sleeping man next to her snorted and shifted in his seat. Thankfully, he'd been like that for most of the flight. She never liked talking on public transport unless she had instigated the conversation, usually for professional reasons.

She couldn't believe how quickly she cleared immigration. It had been half a dozen years since she'd last set foot in America, and her abiding memory of arrival had been spending the thick end of an hour shuffling forward foot by foot in an endless queue that snaked across the concourse while sadistic immigration officers with faces impassive as hatchets questioned every new arrival. As she collected her luggage, she wondered idly what had brought about the change. It couldn't be that the Americans had become less xenophobic or less paranoid about terrorism, that was for sure, especially after Oklahoma. She only had to think about the drop in the numbers of American tourists to Britain in the wake of the IRA's abandoning of their precarious ceasefire.

Slinging her suit carrier across her shoulder, the woman headed for the taxi rank and gave the name of the hotel where she hoped a room would be waiting for her. Even though she'd been up all night, she feared that sleep would abandon her as soon as her head hit the pillow. It didn't matter. She had time. According to her briefing, the best opportunity she'd have wouldn't come before six in the evening of the following day.

She'd heard about the fog rolling in across the bay in the late afternoon, but she'd never quite believed it could be so tangible a phenomenon. She sat among the Sunday tourists in one of the Fisherman's Wharf caf¨¦s and watched the bank of fog envelop the rust-red curve of the Golden Gate, leaving the twin towers stranded above and below. She stirred the last inch of her cappuccino. It had been about the only thing she'd recognized on a list of beverages. They didn't have iced mocha latte in the coffee bar where she picked up her morning carton of steaming pale brown liquid that smelled mostly of its polystyrene container. She supposed this was what they called culture shock.

She'd spent the morning on a whistle-stop sightseeing tour of the crucial highlights. None of her clients had ever sent her to San Francisco before, and she always liked to make the most of her trips at other people's expense. Her one regret was that she hadn't had time for Alcatraz. Now she was reading through her brief one last time, making sure there wasn't something important she'd failed to notice. But it was all as she remembered it. The photographs - well, snapshots really. Directions to the target's home. Suggested lines of approach. And the number to call when she'd achieved her mission.

The woman swallowed the dregs of her coffee and headed back to her hire car, shivering as the damp air hit her. She was wearing only a light cotton shirt over the linen shorts she'd bought for last year's Greek island holiday. It had seemed an appropriate outfit for the warm sun that had beaten down on her earlier. It was California in July, after all. Now the weather had turned into English autumn, she was hopelessly underdressed. She wondered whether she had time to slip back to her hotel, but decided against it.

Ten minutes out of the city, and she was as glad of her decision as she was of the car's air conditioning. The fog that had chilled her was so localised that half a dozen miles away people were still sweating in the same heat that had engulfed her earlier in the day. But at least the air conditioning meant she was clear-headed enough to pay attention to the road signs, making sure she ended up heading down the coast on Highway 1. She drove cautiously, aware that a speed limit lower than the UK's would be easy for her to breach without realizing. Attracting the attention of the Highway Patrol would definitely not be a good idea.

The road curved across the peninsula past the vast suburban tract of Daly City, then swerved toward the ocean, the blue swell coming properly into view as she rolled down the hill and past the boxy condos of Pacifica. According to the map she had unfolded on the passenger seat, she was nearly halfway there. Once the map ran out, she had a hand-drawn map of her exact destination, courtesy of her client.

She appreciated the need for the detailed map as soon as she turned off the highway into Half Moon Bay. She found herself in a grid of streets between highway and ocean, quiet residential streets where a strange car cruising slowly and making wrong turns would probably be noticed before too long. Following her directions, she turned on to a road fronting the Pacific. The houses were detached, two storeys high, covered in either carefully tended white or pastel siding or natural wood protected from the climate by heavy coats of sealant. Several had verandas along the front that looked out across the calm ocean toward the eventual sunset. The houses looked like money. Not excessive, obscene, vulgar amounts, but substantial, two professional income levels. As she approached the house where her target lived, she was careful neither to speed up nor to slow down, but she slewed her eyes left as she passed and registered a battered black convertible in the drive. According to the client, that was the target's car. As expected, she wasn't home. But this wasn't an appropriate place. Too easy for her target to avoid what came next.

The woman carried on to the end of the road and turned left on to the rough, unmetalled track that led across the few hundred yards of greenish-brown scrub that lay between the houses and the dunes that edged the beach. As she drew nearer, she could see what had looked like a gentle swell breaking on the sand in a white frothing surf. Where the track ended there was a clear area, and, as instructed, she parked her hire car there, a short distance from the two other vehicles already facing the pounding waves.

She got out of the car and ignored the hard-packed path that led from the car park to the beach. Instead, the woman walked about half a mile north across the scrub before she chose another route down to the beach. She didn't go all the way down, halting at a point where, if she hunkered down, she would be invisible both from the beach and the flat scrubland above. She settled behind an outcropping of gritty sandstone and surveyed the long sweep of the strand. She'd never seen so spectacular a beach that wasn't scarred with serried ranks of sun loungers, parasols, cars, and bars. The beach was wide and flat, sweeping round in a long white arc. From the air, it would look more like a crescent than a half moon, scything a thick line between the dark blue sea and the brown land.

She took a small pair of green rubber binoculars from her satchel and scanned the beach from north to south. Luckily for her purpose, there were surprisingly few people, and those there were clearly didn't belong to the bucket and spade brigade. Every time the woman's binoculars picked out a dog, she paused and took a careful look at the animal and its owner. There was no sign of her target.

The woman lowered her binoculars and waited five minutes before repeating the exercise. On the third sweep, she picked out the black Labrador frolicking in the waves. In spite of his playfulness, he was clearly no puppy. She felt a frisson of excitement. Forcing herself to be patient, she continued her slow scan. A couple of hundred yards behind the dog, a figure jogged slowly. A finger nudged the focus wheel and the face came into sharp focus. There was no doubt about it. It matched the pictures supplied by her client. The dog was a six-year-old Labrador-cross called Mutton. The woman was a thirty-seven-year-old journalist with a reputation for stirring up trouble. Her name was Lindsay Gordon. If the observer was successful in her mission, tomorrow someone else would have to walk the dog.

With infinite care, the watcher returned the binoculars to the backpack. It was time to do the business.