The novel opens as Poirot receives a summons at his breakfast table from England's premier physicist, Sir Claud Amory. Busy working on a new formula necessary for England's defense in the Second World War, Amory suspects a member of his household of espionage. Of course, by the time Poirot and sidekick Hastings arrive at the scientist's country house, he is suddenly and mysteriously dead.

In the middle of the night in rural Scotland, Michael Starkwedder has run his car into a ditch and must go to the nearest house to seek help. But downstairs in this house, he discovers a murdered man in a wheelchair and a woman holding a recently fired gun. What seems obvious isn't, and the story that unfolds is classic Christie - a tangled web of lies and coverups, where nothing can be taken at face value, and the murderer, and motive, is the greatest...