Ten people are invited to a summer party on an island oft the Devon coast. They are an extremely varied group from a blustering major to a frigid spinster. The only thing they have in common is that they were each involved in a case of unexpected death. They soon find something very odd about their invitations, and then they start to die, one by one. But who is the murderer and where is he hiding.

Jonathan Dakers' early ambition was to become a great surgeon and to marry Edie Martyn. But, on the death of his father, he is obliged to start work as a partner in a poor general practice in the Black Country. Edie falls in love with Jonathan's brother, Harold, who is killed in the Great War, and Jonathan marries her as planned. It is only afterwards that he realises he now loves another.

Bedelia Carrington is living happily, it appears, in Monte Carlo with her husband Charlie Carrington. But a cultivated young artist, Ben Chaney, begins probing into her past with curious concern. Chaney, who is really a detective, learns that Bedelia's obsession for money has led her, in the past, to husband-poisoning for the insurance money.