During an annual board of trustees meeting, one of the trustees dies. Miss Marple thinks he's been poisoned after finding a chemical on him. She sets off to investigate at the ship where he had just come from. The fourth and final film from the Miss Marple series starring Margaret Rutherford as the quirky amateur detective.
A murderer is brought to court and only Miss Marple is unconvinced of his innocence. Once again she begins her own investigation.
Miss Marple believes she's seen a murder in a passing-by train, yet when the police find no evidence she decides to investigate it on her own.