After Colonel Reginald Adams and his actress wife Anne-Marie have forbidden their young daughter Ruby to marry American communist John Van Ert Anne-Marie is found drowned. Inspector Valentine believed she fell in the lake whilst drunk but Father Brown proves it was murder. Learning that the couple argued, Valentine arrests Reginald just as Anne-Marie's long-lost brother James Trewlove arrives from Nairobi. Anne-Marie's will leaves James nothing, with the chief beneficiary being the church whilst Ruby is bequeathed the Flying Stars,a valuable necklace. During a performance of a play at the Adams' house the necklace is stolen. Father Brown manages to unmask both thief and Anner-Marie's killer.