Based on

Movies like Dopey Dicks (1950)

The stooges become detectives and go to the aid of girl in the clutches of a mad scientist. The boys arrive at a spooky mansion where the madman is building a mechanical man that needs a human head. After declining the opportunity to supply a stooge-head for the experiment, they find the girl and escape, only to wind up in a car driven by the headless robot.