Alastair Sim and Trevor Howard star in this gripping suspense story set in a wartime emergency hospital near London, where a local postman, a casualty of a German bombing raid, mysteriously dies on the operating table. A nurse, one of six medical personnel present in the operating room on the night of the postman's death, stumbles upon evidence of murder and is stabbed to death. An inspector from Scotland Yard, in the person of Alastair Sim, arrives to investigate and discovers that each of the remaining five suspects has an excellent motive for both of the murders. In an edge-of-your-seat scene, the detective stages a mock operation which reconstructs the crime and dramatically unmasks the killer.