In Casablanca, Morocco in December 1941, a cynical American expatriate meets a former lover, with unforeseen complications.
When American writer Mark Halliday visits the very married Margot Wendice in London, he unknowingly sets off a chain of blackmail and murder.
Having met on a train, a smooth-talking psychotic socialite shares his theory on how two complete strangers can get away with murder to an amateur tennis player — a theory he plans to test out.
