When a stranger runs his car into a ditch in dense fog near the South Wales coast, and makes his way to an isolated house, he discovers a woman standing over the dead body of her wheel-chair bound husband, gun in her hand. She admits to murder, and the unexpected guest offers to help her concoct a cover story.

But is it possible that Laura Warwick did not commit the murder after all? If so, who is she shielding? The victim's retarded young half-brother or his dying matriarchal mother? Laura's lover? Perhaps the father of the little boy killed in an accident for which Warwick was responsible? The house seems full of possible suspects ...

Charles Osborne has adapted the novel from Agatha Christie's original play of the same title from 1958.