Q.E.D. (1922) is a mystery novel written by Lee Thayer. The story revolves around the murder of a wealthy businessman, John Ferguson, who is found dead in his office. The investigation is led by Detective Fleming Stone, who is assisted by his friend and amateur detective, Philo Vance. As the investigation progresses, a number of suspects emerge, including Ferguson's business partner, his secretary, and his wife. The detectives must navigate a web...