A theatrical magnate celebrates his seventieth birthday by announcing his will and a planned marriage between his niece and his managing director; shortly after, a murder shocks the household and a family member becomes the prime suspect. Joan undertakes a private investigation, aided by a long-standing friend and a young ally, and uncovers overlooked clues that prompt police re-evaluation. The narrative alternates courtroom tension, methodical inquiry, and personal confrontations, with a small but telling physical clue altering the course of the case. The mystery resolves with the accused freed and relationships and finances rearranged toward a domestic and romantic conclusion.