Clarissa, the wife of a Foreign Office diplomat, is given to daydreaming. 'Supposing I were to come down one morning and find a dead body in the library, what should I do?' she muses. Clarissa has her chance to find out when she discovers a body in her drawing-room. Desperate to dispose of the body before her husband comes home with an important foreign politician, Clarissa persuades her three house guests to become accessories and accomplices. The search begins for the murderer and the motive, while at the same time trying to persuade a police inspector that there has been no murder at all.