 Lawyer Perry Mason is summoned to the Laxter mansion in the dead of night to write granddaughter Wilma out of invalid Peter Laxter s will, to keep her from marrying suspected fortune hunter Doug. Peter dies in a mysterious fire and Laxter s two grandsons, Sam Laxter and Frank Oafley, inherit his estate on the condition old caretaker Schuster and his cat Clinker are kept on. When cat-hating Sam threatens Clinker, Perry steps in and learns Laxter s death was suspicious and the family fortune and diamonds are missing. Schuster s found dead in his basement apartment, Laxter s nurse Louise is murdered with Schuster s crutch, and circumstantial evidence brings Doug to trial for Louise s death. Mason s investigation produces a surprise witness who turns the trial around.