It always feels good when you find a way of telling the story that seems to reflect and amplify the larger themes. In this case, the story is about a woman who lies in court to help the police convict the man they think raped and killed her best friend. I wanted to focus the plot on that simple moral issue - is it ever right to lie, and what happens if you get it wrong? But I also wanted to construct the book so that the question of whether or not the heroine, Ros, actually understands what really happened feeds into a whole series of questions about truth and lies. So, for example, it felt very natural to have the book narrated alternately by Ros and her policeman lover, allowing the reader to see smaller instances where their versions of events contradict each other. And the fact that she's dealing with fakes at work, in her job as a picture restorer at the National Gallery, seemed both to fit thematically and to create some neat plotting, when she starts to use her professional skills to unravel what really happened to her friend.

Picasso said "All art is a lie that reveals a greater truth." Funnily enough, the protagonists in thrillers usually have to do exactly the opposite - to find the truth that reveals a lie. Out of that irony I tried to construct a whole cats-cradle of truth and fiction, without ever making the reader feel that the ideas are starting to crush the story.

Tell Me Lies had its genesis in two conversations. One was when a film director, who had optioned a screenplay I had written, told me a story over lunch about a friend of hers who had been tangentially involved in a very famous murder trial. This friend shared a flat near the victim's house and had been visited by a detective who asked if she had seen anything suspicious on the day of the murder. She hadn't, but the two of them hit it off and - completely against the rules - he began a sexual relationship with her. Later in the investigation he told her that the police knew who did it, but couldn't prosecute because the CPS were demanding more corroborating evidence to add to the "rock solid" forensic evidence the police already had. He then persuaded her to make a false statement identifying his suspect as someone she'd seen in the vicinity at the time of the murder. Later, at the trial, it tuned out the forensic evidence wasn't quite as solid as the policeman had believed…. I knew, instantly, that this was something I wanted to turn into a book, but I wasn't quite sure how. The other conversation was with Paul Britton, the eminent forensic psychologist and writer, whom I sat next to at a publisher's dinner a couple of weeks later. I had already based one of my books - The Decoy - on a case he'd been involved with, something he was very gracious about. Paul mentioned that most of his work at that time was with policemen who were suffering from burn-out, and described as one of the symptoms a persistent feeling on the part of the sufferer that he was a fraud, that everyone else was coping fine and that he must pretend to as well, in order not to let the side down. From this conversation my detective, Bill Thomson, was born - a knight in tarnished armour whose desire to protect Ros from harm and to avenge her rape misfires, and ultimately results in her being exposed to much more danger.