When elderly Miss Jane Marple (Margaret Rutherford) witnesses a murder on a train passing next to the one she is on, she is unable to convince the police of what she has seen and must investigate on her own. Deducing that the body has to be buried on land adjacent to the track that is part of Ackenthorpe Hall, she cons her way into a job as a housemaid for the estate in an effort to locate the body and catch the killer.