Mr. Stout, who weighs 350, and his wife, who weighs 100, read the advertisement of Prof. Biff Conners that he can make fat people thin and thin people fat. So also do Mr. and Mrs. Slim, who weigh 110 and 400 respectively. They visit the professor's and there he and his pretty assistant, Pearl, induce all four of them to take up a course. The professor has a way of manipulating the scales to suit his purpose and his clients believe they are either gaining or losing weight. In the course of training at the gymnasium, young Mr. Slim puts a pound dumbbell in each of his boxing gloves and proceeds to box with Mr. Stout. He knocks him out. Others interfere and are accorded the same treatment. The professor, hearing the racket, comes in and he gets the same does. Pearl runs out for a cop and the minion of the law is accorded the same treatment. Eventually all is straightened out and the fat and thin couples go home, resolved that they can do nothing to help their condition and resume.
—Moving Picture World synopsis