In The Eccentric Millionaire Murder Case, Mr. Keen, the renowned investigator, is approached by a distraught man named Mr. Prigg, who reveals that his half-brother, Otis Prigg, has been found murdered in his Pennsylvania mansion. Otis, a multimillionaire known for his eccentric lifestyle, had been living alone in a large, cluttered house, and his death is shrouded in mystery. Mr. Prigg is visibly shaken, having not seen his brother in years, and he explains that Otis had tried to contact Mr. Keen just before his death, which adds an urgent layer to the case.