The New York Times bestselling author of The Monogram Murders and Woman with a Secret returns with a disturbing tale of psychological suspense and obsession that hits at the heart of some of our most precious relationships. 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, and killing them one by one. Before they die, each victim is given...