In Edwardian era London, in the summer of 1903, a Scottish shopowner in Fulham is stabbed to death and his shop set on fire by distinguished composer George Harvey Bone (Laird Cregar), who stumbles out onto the street in a stupor. George eventually makes his way back the next night to his English basement at 12 Hangover Square in Chelsea, London to find his girlfriend Barbara Chapman (Faye Marlowe) and her father Sir Henry Chapman (Alan Napier) inside. George admits privately to Barbara that there is "a whole day missing" from his memory. The newspaper has stories of the murder and fire, and George goes to see Dr. Allan Middleton (George Sanders) who works at Scotland Yard. Bone tells Middleton that when he is stressed or overworked he suffers from periods of amnesia brought on by discordant sounds. Middleton's advice is to go out among ordinary people and observe how they work and recreate.