iona walked through the door to the sound of REM telling her that nobody loved a sad professor. As usual, Kit had stacked up half a dozen CDs in the player in his study, hit the random button and walked out the door while there were still hours of playing time left. He couldn't abide silence. She had learned this early on in their relationship, when she'd taken him walking in her beloved Derbyshire and had been horrified to watch him filling his backpack with cassettes for his Walkman. More than once, she'd come home to an empty house where music spilled out of Kit's study, the TV in the living room blared like a bull and the radio in the kitchen added a mad counterpoint to the racket. The louder the din, the easier he seemed to find it to escape into his own imagined universe. For Fiona, who needed silence in order to concentrate on anything vaguely creative, it was an incomprehensible paradox.

When they'd first talked about living together, Fiona had insisted that whatever property they bought, it had to be capable of providing her with a quiet space to work in. They'd ended up with a tall thin house in Dartmouth Park whose previous owner had been a rock musician. He'd converted the attic into a soundproof studio that provided Fiona with the perfect eyrie to escape Kit's background racket. It was even big enough to allow her to install a futon for those nights when Kit was up against a deadline and needed to write into the early hours of the morning. Sometimes she felt deeply sorry for their long-suffering neighbours. They must dread February when, invariably, the end of a book and late-night Radiohead loomed.

Fiona dropped her bags and went into Kit's ground-floor study to turn off the music. Blessed silence fell like balm on her head. She continued upstairs, stopping off in their bedroom to shuck off her walking gear and pull on her house clothes She trudged up the remaining two flights to her office, feeling the hills in the pull of her leg muscles. The first thing she registered was the flashing light of the answering machine. Fifteen messages. She'd put money on them all being from journalists, and she wasn't in the mood to listen to them, never mind to respond. This was one occasion where she was absolute in her determination not to provide a single quote that could be twisted to suit someone else's agenda.

Leaving her laptop by the desk, Fiona noticed that Major Berrocal hadn't wasted any time. A pile of paper lay accusingly in the fax tray. That she couldn't ignore. Stifling a sigh, she picked it up, automatically straightening the edges, and headed back downstairs.

As Kit had promised, her dinner sat in the fridge. She wondered fleetingly how many of his fans would credit that the man who created scenes of graphic violence that gave critics nightmares was the same creature whose idea of relaxation after a hard day's writing was to cook gourmet food for his lover. They'd probably prefer to believe he spent his evenings on Hampstead Heath, biting the heads off small furry animals. Smiling at the thought, Fiona poured herself a glass of cold Sauvignon while she waited for the ri sotto to heat up, then settled down at the kitchen table with the Spanish fax and a pencil. Glancing at the clock, she decided to catch the news headlines before she began the chore of deciphering foreign police reports.

The theme music of the late evening news thundered out its familiar fanfare. The camera zoomed in on the solemn face of the news reader "Good evening. The headlines tonight. The man accused of the Hampstead Heath murder walks free after a judge accuses the police of entrapment." Top item, Fiona noted without surprise. "Middle East peace talks are on the verge of breakdown in spite of a personal intervention by the US President. And the rouble tumbles as fresh scandal hits Russia's banking system."

The screen behind the news reader head changed from the programme logo to a shot of the exterior of the Central Criminal Court. "At the Old Bailey today, the man accused of the savage rape and murder of Susan Blanchard was freed on the order of the trial judge. Mrs. Justice Mary Delancey said there was no doubt that the Metropolitan Police had entrapped Francis Blake in an operation which she described as "little short of a witch-hunt". In spite of the lack of any solid evidence against Mr. Blake, she said, they had decided that he was the killer. Over to our Home Affairs Correspondent, Danielle Rutherford, who was in court today."

A woman in her thirties with mouse-brown hair tangled by the wind gazed earnestly at the camera. "There were angry scenes in court today as Mrs. Justice Delancey ordered the release of Francis Blake. The family of Susan Blanchard, who was raped and murdered as she walked on Hampstead Heath with her twin babies, were outraged at the judge's decision and at Blake's obvious jubilation in the dock.

"But the judge was unmoved by their protests, saving her condemnation for the Metropolitan Police whose methods she described as an affront to civilized democracy. Acting on the advice of a psychological profiler, the police had set up a sting using an attractive female detective in an attempt to win Mr. Blake's affections and to lure him into confessing to the murder. The sting, which cost hundreds of thousands of pounds of the police operations budget and lasted for almost three months, did not lead to a direct confession, but police believed they had obtained sufficient evidence to bring Mr. Blake to trial.

"The defence argued that whatever Mr. Blake had said had been at the instigation of the female detective and had been calculated to impress the personality she had falsely projected. And this view was upheld by the judge. After his release, Mr. Blake, who has spent eight months in prison on remand, announced he would be seeking compensation."

The picture changed, revealing a stocky man in his late twenties with cropped black hair and deep-set dark eyes. A forest of microphones and hand-held tape recorders blossomed in front of his white shirt and charcoal suit. His voice was surprisingly cultivated and he glanced down frequently at a piece of paper in his hands. "I have always protested my innocence of the murder of Susan Blanchard, and today I have been vindicated by a court of law. But I have paid a terrible price. I have lost my job, my home, my girlfriend and my reputation. I am an innocent man, but I have spent eight months behind bars. I will be suing the Metropolitan Police for false imprisonment and for compensation. And I sincerely hope they will think twice before they set about framing another innocent man." Then he looked up, his eyes blazing anger and hatred. Fiona shivered involuntarily.

The picture changed again. A tall man in a crumpled grey suit flanked by a pair of stony-faced men in raincoats walked towards the camera, head down, mouth drawn into a thin line. The reporter's voice said, "The police officer in charge of the case, Detective Superintendent Steve Preston, refused to comment on Blake's release. In a later statement, New Scotland Yard announced they were not actively seeking anyone else in connection with Susan Blanchard's murder. This is Danielle Rutherford at the Old Bailey."

Back in the studio, the news reader announced that there would be an in-depth look at the background to the case after the break. Fiona turned off the TV. She had no need of their potted version of the facts. There were powerful reasons why she would never forget the rape and murder of Susan Blanchard. It wasn't the graphic police photographs of the body or the pathologist's report or her knowledge as a local resident of the scene of the crime, a mere twenty-minute walk from her own front door, although all of these had been terrible enough. Nor was it the brutality of a killer who had violated and stabbed a young mother in full view of her eighteen-month-old twin sons.

What made the Hampstead Heath murder so significant for Fiona was that it had marked the end of her association with the Met. She and Steve Preston had been close since their undergraduate days when they'd both read psychology at Manchester. Unlike most student friendships, it had persisted in spite of their very different career paths. And when British police forces had first started to consider the potential advantages of working with psychologists to improve their chances of catching repeat offenders, it had seemed the most natural thing in the world for Steve to consult Fiona. It had been the start of a fruitful relationship, with Fiona's rigorous approach to data analysis complementing the experience and instincts of the detectives she had worked with.

Within hours of the discovery of Susan Blanchard's body, it had been clear to Steve Preston that this was precisely the kind of case where Fiona's talents could be used to best advantage. A man who could kill like this was no beginner. Steve had learned enough from listening to Fiona, supplemented by his own reading, to know that such a killer would already have cast his shadow over the criminal justice system. With her expertise, Fiona would be able to suggest at the very least what sort of record their suspect would have. Depending on the circumstances, she might well be able to indicate the geographical area he'd be likely to live in. She would look at the same things that detectives saw, but for her they would have different meanings.

Early in the investigation, Francis Blake had emerged as a possible suspect. He had been seen on the Heath around the time of the murder, running away from the direction of the dense undergrowth that shielded the small clearing where Susan Blanchard's body had been found by a dog-walker who heard the children crying. Blake was branch manager for a firm of undertakers, which suggested to detectives that he had an unhealthy preoccupation with the dead. He had also worked in a butcher's shop as a teenager, which the police decided meant he was comfortable with the sight of blood. He had no adult criminal record, although he had been cautioned twice as a juvenile, once for setting fire to a rubbish bin and the second time for an assault on a younger boy. And he was evasive about what he'd been doing on the Heath that morning.

There was only one problem. Fiona didn't think Francis Blake was the killer. She said so to Steve and she kept on saying so to anyone who would listen. But her suggestions for alternative lines of inquiry had apparently led nowhere. Under the glare of an outraged media, Steve was under pressure to make an arrest.

One morning he'd turned up at her office at the university. She'd taken one look at the hard set of his features and said, "I'm not going to like this, am I?"

He shook his head and dropped into the chair facing her. "You're not the only one. I've argued till I was blue in the face, but sometimes you just can't buck the politics. The Commander's gone over my head. He's brought in Andrew Horsforth."

Neither of them needed to comment. Andrew Horsforth was a clinical psychologist. He had worked for years in a secure mental hospital whose reputation had slumped with every independent report ever made into it. He relied on what Fiona contemptuously referred to as the 'touchy-feely' approach to profiling, priding himself on the quality of insights gained from years of hands-on experience. "Which would be fine if he could ever see past his own ego," she'd once commented sarcastically after listening to him lecture. He'd had what she privately referred to as a lucky break on the first major case where he'd produced a profile and he'd traded on it ever since, never failing to provide the media with all the quotes and interviews they could desire. When police made an arrest on a case where he'd produced an offender profile, he was always quick to claim the credit; when they failed, it was never his fault. Faced with Francis Blake as a suspect, Fiona felt certain Horsforth could make the profile fit the man.

"I'm out of it, then," she said with an air of finality.

"Believe me, you're well out of it," Steve said bitterly. "They've decided to ignore your professional advice and my personal opinion. They're going ahead with the sting. Orchestrated by Horsforth."

Fiona shook her head in exasperation. "Oh, for fuck's sake," she exploded. "It's a terrible idea. Even if I thought Blake was your man, it would still be a terrible idea. You might just get something that would stand up in court if you used a trained psychologist with years of experience of therapeutic work to do the entrapment, but with the best will in the world, setting some young copper loose with an idiot like Horsforth briefing her is a recipe for disaster."

Steve ran his hands through his thinning dark hair, pushing it back from his forehead. "You think I haven't told them that?" His mouth clamped shut in a frustrated line.

"I'm sure you have. And I know you're as pissed off about it as I am." Fiona got to her feet and turned to look out of the window. She couldn't bear to show her humiliation, even to someone as close as Steve. "That's it, then," she said. "I'm finished with the Met. I'm never going to work with you and your colleagues again."

Steve knew her well enough to realize there was little point in trying to argue when she was in this frame of mind. He'd been so angry at the dismissal of his own professional judgement that the thought of resignation had briefly flashed across his mind. But unlike Fiona, he had no alternative career where his expertise could make a difference, so he'd tossed the notion aside impatiently as the self-indulgence of hurt pride. He hoped Fiona would do the same, given time. But this wasn't the moment to suggest that. "I can't blame you," he said sadly. "I'll be sorry to lose you."

Composed again, she faced him. "I'm not the only one you'll be saying sorry to before this is over," she'd said mildly. Even then, she'd understood how badly things could turn out. Police officers desperate for an arrest, shored up by the seeming respectability of a psychologist who told them what they wanted to hear, would not be satisfied till they had their man behind bars.

It gave her no pleasure at all to see how right she'd been.