Adapted from Agatha Christie's play The Unexpected Guest. In rural Wales, a passerby discovers a man murdered and a house full of people with good reason to have murdered him.

Agatha Christie is the most widely published author of all time with her works outsold only by Shakespeare and the Bible. She is regarded by generations of fans as the greatest mystery writer ever, and her novels are read and cherished the world over.

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.