When someone shoots Horatio Leavenworth, a wealthy retired merchant, through the head in his library late one night, the evidence at the inquest indicates that no one could have left the victim's locked Manhattan mansion before the discovery of the body the next morning. Suspicion thus falls on members of the household, specifically the dead man's nieces, Mary and Eleanore, only one of whom stands to benefit from their uncle's death. Everett Raymond, a junior partner in a New York law firm that had Leavenworth as a client, teams with unassuming official investigator Ebenezer Gryce to seek the truth.