From its opening sentences Susanna Moore's new novel alerts the reader to its possibilities:

I don't usually go to a bar with one of my students. It is almost always a mistake.

But Cornelius was having trouble with irony. For a cop book, which at its basest level this is, that is pretty good. This is where Moore shines. Her heroine is a faintly prissy-looking, bespectacled thirty-four-year-old English teacher who is writing a monograph on Portuguese words in Rhode Island slang. An unlikely heroine for an erotic thriller. Usually the word 'erotic' in the blurb means there are some dirty bits which someone else's grandmother might dislike; in this case, 'erotic' means verging on the pornographic, but pornography with a point. It is her heroine's growing sexual obsession with a caricature Irish cop which leads her into disaster.

The narrator - we never learn her name – walks into danger when, looking for a lavatory in the bar to which she has taken her student, she witnesses a redheaded woman giving a man a blow-job. Hours later the redhead is found murdered and the police are at the