The New York Times bestselling author of The Monogram Murders and Woman with a Secret returns with a disturbing tale of psychological suspense that revolves around a chilling question: What if having a best friend could put you in the crosshairs of a killer?A psychopath the police have dubbed “Billy Dead Mates” is targeting pairs of best friends, killing them one by one. Before they died, the victims all received a small white book, blank except for two lines of text—different messages chosen specifically for each victim. For months, detectives have failed to catch the elusive criminal, devise a solid motive, or figure out what the white books symbolize and why the killer creates them for his prey. Though law enforcement has Billy’s DNA—he leaves it on a teacup at the scene of each crime—they haven’t been able to identify him or discover any other clues. As the days tick by, the detectives on the case are driven closer to the edge while the public grows increasingly panicked. Then a woman, disturbed by a police request on the news, comes forward. What she reveals shocks the investigators and adds another troubling layer to an already complex case.Kim Tribbeck, a stand-up comedian, received one of those peculiar little books. A stranger gave it to her at one of her gigs last year. Was the stranger the psycho killer? Kim has no friends and trusts no one, so how—and why—could Billy Dead Mates care about her? But if she’s not in his crosshairs, then why was she given one of those strange books? And who will be the next to die?Sophie Hannah raises the stakes with each successive page in this haunting and twisting thriller that reaffirms her place as one of today’s most talented suspense writers.