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.