A tall chalk escarpment rose steeply on either side of the train. Then to his left it gave way to houses and a park. In moments they would be approaching Brighton station. There wasn’t enough time to check the CD out now; he would have a look at home later tonight, he decided.

If he could have had the smallest inkling of the devastating impact it was going to have on his life, he would have left the damned thing on the seat.

Squinting against the low evening sun, Janie eyed the clock on the dash of her Mini Cooper in panic, then double-checked it against her wristwatch. 7.55 p.m. Christ. ‘Almost home, Bins,’ she said, her voice tight, cursing the Brighton seafront traffic, wishing she’d taken a different route. Then she popped a tab of chewing gum into her mouth.

Unlike his owner, the cat had no hot date tonight and was in no hurry. He sat placidly in his wicker carrying basket on the front passenger seat of the car, staring a tad morosely out through the bars at the front – sulking perhaps, she thought, from having been taken to the vet. She put out a hand to steady the basket as she turned, too fast, into her street, then slowed down, looking for a parking space, hoping to hell she was going to be lucky.

She was back a lot later than she had intended, thanks to her boss keeping her on in the office – today of all days – to help draft briefing notes for a conference with counsel in the morning on a particularly bitter divorce case.

The client was an arrogant, good-looking layabout who had married an heiress and was now going for as much of her money as he could get. Janie had loathed him from the moment she first met him, in her boss’s office some months back; in her view he was a parasite, and she secretly hoped he would not get one penny. She had never confided her opinion to her boss, although she suspected he felt much the same.

Then she had been kept over half an hour in the vet’s waiting room before finally being ushered in with Bins to see Mr Conti. And it really had not been a successful consultation. Cristian Conti, young and quite hip for a vet, had spent a lot of time examining the lump on Bins’s back and then checking elsewhere. Then he had asked her to bring the cat back in tomorrow for a biopsy, which had immediately panicked Janie into worrying that the vet suspected the lump was a tumour.

Mr Conti had done his best to allay her fears and had listed the other possibilities, but she had carried Bins out of the surgery under a very dark shadow.

Ahead she saw a small space between two cars, a short way down from her front door. She braked and put the car into reverse.

‘You OK, Bins? Hungry?’

In the two years since they had become acquainted, she had grown very attached to the ginger and white creature, with his green eyes and huge whiskers. There was something about those eyes, about his whole demeanour, the way one moment he would nuzzle up to her, purring, sleeping with his head on her lap when she watched television, and another moment he was giving her one of those looks that seemed so damned human, so adult, so all-knowing. He was so right, whoever it was who had said, ‘Sometimes when I am playing with my cat, I wonder if perhaps it is not my cat who is playing with me.’

She reversed into the space, making a total hash of it, then tried again. Not perfect this time either, but it would have to do. She closed the sunroof, picked up the cage and climbed out of the car, pausing to check her watch one more time, as if somehow, miraculously, she had read it wrong last time. She hadn’t. It was now one minute to eight.

Just half an hour to feed Bins and get ready. Her date was a control freak, who insisted on dictating exactly how she looked each time they met. Her arms and legs had to be freshly shaven; she had to put on exactly the same measure of Issey Miyake and in the same places; she had to wash her hair with the same shampoo and conditioner, and apply exactly the same make-up. And her Brazilian had to be trimmed to within microscopic tolerances.

He would tell her in advance what dress to wear, what jewellery, and even where in the flat he wanted her to be waiting. It all went totally against the grain; she had always been an independent girl, and had never allowed any man to boss her around. And yet something about this guy had got to her. He was coarse, eastern European, powerfully built and flashily dressed, whereas all the men she had dated previously in her life had been cultured, urbane smoothies. And after just three dates she felt in his thrall. Just even thinking about him now made her moist.

As she locked the car and turned to walk towards her flat she did not even notice the only car in the street not caked in pigeon and seagull guano, a shiny black Volkswagen GTI with blacked-out windows, parked a short way ahead of her. A man, invisible to the outside world, sat in the driver’s seat, watching her through a tiny pair of binoculars and dialling on his pay-as-you-go mobile phone.

Shortly after half past seven Tom Bryce drove his sporty silver Audi estate past the tennis courts, then the open, tree-lined recreation area of Hove Park, which was teeming with people walking dogs, playing sports, lazing around on the grass, enjoying the remnants of this long, early summer day.

He had the windows down, and the interior of the car was filled with gently billowing air carrying the scent of freshly mown grass and the soothing voice of Harry Connick Junior – who he loved, but Kellie thought was naff. She didn’t care for Sinatra either. Quality singing just didn’t do it for her; she was into stuff like house, garage, all those weird beaty sounds he did not connect to.

The longer they were married, the less it seemed they had in common. He couldn’t remember the last movie they’d agreed on, and Jonathan Ross on a Friday night was about the only TV show they regularly sat down to watch together. But they loved each other, that he was sure of, and the kids came above everything. They were everything.

This was the time of each day he enjoyed the most, the anticipation of getting home to the family he adored. And tonight the contrast between the vile, sticky heat of London and the train, and this pleasant moment now seemed even more pronounced.

His mood improving by the second, he crossed the junction with swanky Woodland Drive, nicknamed Millionaires’ Row, with its long stretch of handsome detached houses, many backing onto a copse. Kellie hankered to live there one day, but it was way out of their price league for the moment – and probably always would be, the way things were headed, he thought ruefully. He continued west, along the altogether more modest Goldstone Crescent, lined on either side with neat semi-detached houses, and turned right into Upper Victoria Avenue.

No one was quite sure why it had been named Upper since there was no Lower Victoria Avenue. His elderly neighbour, Len Wainwright – secretly nicknamed the Giraffe by Kellie and himself, as he was nearly seven foot tall – had once announced in one of his many moments of not exactly blinding erudition across the garden fence that it must be because the street went up a fairly steep hill. It wasn’t a great explanation, but no one had yet come up with a better one.

Upper Victoria Avenue was part of a development which was thirty years old but still did not yet look as if it had reached maturity. The planes in the street were still tall saplings rather than full trees, the red brick of the two-storey semi-detached houses still looked fresh, the mock-Tudor wood beams on the roof facings hadn’t yet been ravaged by woodworm or the weather. It was a quiet street with a small parade of shops near the top, mostly lived in by youngish couples with kids, apart from Len and Hilda Wainwright, who had retired here from Birmingham on their doctor’s suggestion that the sea air would be good for Hilda’s asthmatic chest. Tom held the view that cutting down on her forty fags a day might have been a better option.