A mother confronts a former hangman, Henry Lee, at his wedding anniversary about her son he executed, for murdering a court secretary, a year ago. An execution where the condemned man whispered to Lee who the killer was. The following morning Lee is poisoned with Hemlock. His friend George, an ex policeman, is arrested and released. The mother, recently released from prison, is arrested and a motive for Lee's wife emerges. Father Brown untangles a web of deceit and corruption in the police as Lee lays dying.