An elderly lady is on her way to Scotland Yard to report several murders in her village. "It is very easy to kill, so long as no one suspects you," she tells the man she meets on the London train, retired policeman Luke Fitzwilliam. He ascribes it all to a vivid imagination and hopes they'll let the old dear down lightly. That is, until he learns about two more suspicious deaths - one of which is the old lady's.