A young man, broken down in the fog, witnesses a murder he is asked to conceal. A full-length novel adapted by Charles Osborne from Agatha Christie's acclaimed play.When a stranger runs his car into a ditch in dense fog in South Wales and makes his way to an isolated house, he discovers a woman standing over the dead body of her wheelchair-bound husband, gun in her hand. She admits to murder, and the unexpectedguest offers to help her concoct a cover story.