A must-read for fans of Clare Mackintosh and Paula Hawkins.'Sophie Hannah is genuinely Christie's heir' The Scotsman'Hugely entertaining, full of uncomfortable truths' London Evening StandardWhat if having a best friend was the most dangerous thing you could do?A killer that the police are calling 'Billy Dead Mates' is murdering pairs of best friends, one by one. Before they die, each victim is given a small white book... For months, detectives have failed to catch Billy, or work out what the white books mean. And then a woman, scared by what she's seen on the news, comes forward.Stand-up comedian Kim Tribbeck has one of Billy's peculiar little books. A stranger gave it to her at a gig she did a year ago. Was he Billy, and does he want to kill her? Kim has no friends and trusts no one, so how - and why - could she possibly be Billy Dead Mates' next target?This is the next chilling novel from the queen of psychological crime - a literary puzzle set to unlock the dark side of the mind . . .