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. She has the chance to find out when she discovers a body … in her drawing-room. Desperate to dispose of it, she attempts to persuade her house guests to become accessories and accomplices. Now, as the search begins for the murderer in their midst, supposing a police inspector arrives…