Dr. Clitterhouse is a wealthy society physician in
New York City who decides to research the medical aspects of the behavior of criminals directly by becoming one. He begins a series of daring jewel robberies, measuring his own blood pressure, temperature and pulse before, during and afterwards, but yearns for a larger sample for his study. From one of his patients, Police Inspector Lewis Lane, he learns the name of the biggest
fence in the city, Joe Keller. He goes to meet Keller to sell what he has stolen, only to find out that "Joe" is actually "Jo". The doctor impresses Jo and a gang of thieves headed by 'Rocks' Valentine with his exploits, so Jo invites him to join them, and he accepts. Dr. Clitterhouse pretends to take a six-week vacation in Europe. As "The Professor", he proceeds to wrest leadership of the gang (and the admiration of Jo) away from Rocks, making him extremely resentful. When they rob a fur warehouse, Rocks locks his rival in a cold-storage vault, but Clitterhouse is freed by Butch, a gang member that Jo had assigned to keep watch on him. Afterwards, Clitterhouse announces he is quitting; he has enough data from studying the gang during their robberies, and his "vacation" time is up. He returns the gang to Rocks's control. Rocks learns Dr. Clitterhouse's real identity and shows up at his
Park Avenue office. Rocks tries to
blackmail the doctor into using his office as a safehouse as they rob the doctor's own wealthy friends. Clitterhouse learns that Rocks will not let him publish his incriminating research, and also realizes that he has not studied the ultimate crime – murder – which will be the final chapter to his book. So, he gives a poisoned drink to Rocks, and he studies his symptoms as he dies. Jo helps dispose of the body in the river, but it is recovered and the poison is detected by the police. The doctor is ultimately caught by his friend, Inspector Lane, and placed on trial. He insists that he did everything for purely scientific reasons and claims that his book is a "sane book" and that it is "impossible for an insane man to write a sane book". His determination to show that he is sane, and therefore willing to face the
death penalty, convinces the jury to find him
not guilty by reason of insanity. ==Cast==