'Happy fifty-third birthday, Doctor. Welcome to the first day of your death. You ruined my life. And now I fully intend to ruin yours.

'You have exactly one fortnight, starting tomorrow morning at 6 a.m., to discover who I am. When you succeed you must purchase one of those tiny ads at the bottom of the New York Times front page, and print my name there.

'If you do not succeed, then . . . you will take note that the second sheet of this letter contains the names of fifty-two of your relatives. If you are unable ... Read moreto purchase the ad as described, then you will have this choice: kill yourself immediately or I will destroy one of these innocent people.'

Until the moment he opens the letter, New York psychologist Dr Frederick Starks has led a quiet and, so he believes, blameless life. He has no idea why he's being judged by this unknown tormentor a former patient - who then lethally begins to demonstrate the potential of his, or her, threats. As the layers of Starks's carefully constructed life are stripped from him, he quickly finds himself a powerless pawn in a psychopath's devious game of vengeance.