A meticulous Scotland Yard detective responds when a distressed young woman insists that a friend's apparent suicide was murder. He assembles witness testimony, timetables, physical traces, and the movements of cars and passengers, pursuing leads across towns and interrogating suspects. The investigation relies on patient, methodical reconstruction of journeys and alibis, surveillance, and legal procedures to reveal how a deliberate theft-and-deception scheme escalated into violence. Ultimately procedural persistence unmasks the perpetrators and resolves the intricate puzzle.