Returning from a Swiss business trip, executive Mark Bretherick finds the dead bodies of his wife Geraldine and daughter in the bathtub. It looks like a suicide, but there's no note or known motive. Country police chief Proust gives the case to recent London transferee, detective sergeant Charlie Zailer. Lacking confidence, she ignores the advice of veteran DC Simon Waterhouse, imagining a conspiracy. Bretherick gets a visit from a strange woman who claims to have had an affair with a man using Mark's name.