Clarissa, the young wife of a Foreign Office Diplomat, delights in tweaking the sensibilities of her more serious friends and for playing a game she calls supposing - imagining a difficult situation and figuring out how people would respond. But Clarissa's lighthearted game becomes deadly serious when she discovers the dead body of an unknown person in her own drawing room. If that wasn't bad enough, her husband is on the way home with an important foreign politician and the attendant scandal of the dead body would irrevocably damage his career at the very least. Therefore, Clarissa decides to dispose of the body and persuades her three houseguests to help. But before she can get the body off the premises, a policeman arrives at her front door. The police received an anonymous tip about a murder in the house and have shown up to investigate. Now Clarissa must keep the body hidden, convince the skeptical police inspector that there has been no murder, and, in the meantime, find out who has been murdered, why, and what the body is doing in her house.