Miss Jane Marple (Dame Margaret Rutherford) investigates the murder of one of her fellow trustees of a fund which rehabilitates young criminals. To investigate she goes aboard the ship used to train the juveniles, much to the distress of Captain Sydney De Courcy Rhumstone (Lionel Jeffries). She soon stumbles onto more murders, and a ring of thieves.—
Margaret Rutherford, Lionel Jeffries, Charles 'Bud' Tingwell
IMDB plot
After Miss Jane Marple is made a trustee of a merchant marine training vessel, a fellow trustee is poisoned, and ship's officers are later murdered after she comes on board.