John L. Sullivan is a popular young Hollywood director of profitable but shallow comedies. Dissatisfied with making such films as Ants in Your Plants of 1939, he tells his studio boss, Mr. LeBrand, that he wants his next project to be a serious exploration of the plight of the downtrodden based on the novel O Brother, Where Art Thou? LeBrand wants him to direct another lucrative comedy instead, but Sullivan refuses. He wants to "know trouble" first hand, and plans to travel as a tramp so he can make a film that truly depicts the sorrows of humanity. His British butler and valet both openly question the wisdom of his plan.
Sullivan dresses as a hobo and takes to the road, followed by staff in a bus imposed on him for his own safety by the studio. Nobody is happy with the arrangement, and Sullivan, after trying to lose the bus in a fast-paced car chase, eventually persuades his guardians to leave him alone and arranges to rendezvous with them later in Las Vegas. However, he soon returns to Los Angeles. There, in a diner, Sullivan meets a struggling young actress who has failed to make it in Hollywood and is just about to give up and go home. She believes he is a penniless tramp and buys him breakfast.
The film's trailerIn return for her kindness, Sullivan retrieves his car from his estate and gives her a ride. He neglects to tell his servants that he has returned, so they report the car stolen. Sullivan and the girl are briefly apprehended by police, but let go after things are cleared up. He and the girl go to his palatial mansion. After seeing how wealthy he is, she shoves him into his swimming pool for deceiving her. However, when he insists on trying again, she goes with him, over his objections, disguised as a boy.
This time Sullivan succeeds. After riding in a cattle car, eating in soup kitchens and sleeping in homeless shelters with the girl (where someone steals his shoes), Sullivan finally decides he has had enough. His experiment is publicized by the studio as a huge success. The girl wants to stay with him, but Sullivan reveals to her that he is married, lovelessly, to someone else, having been advised to do so solely to reduce his taxes. Worse, the plan backfired, with Sullivan's joint returns higher than when he was single and his wife's having an affair with his business manager.
Sullivan decides to thank the homeless for the insights he has gained by handing out $5 bills. At a train yard, a man knocks Sullivan unconscious, steals his money and shoes, and dumps him in a departing boxcar. While escaping with Sullivan's money, the thief gets run over by another train. When the mangled body is found, the ID cards sewn into the stolen shoes identify the deceased as Sullivan.
Sullivan wakes up in another city, with no memory of who he is or how he got there. A yard bull finds him and accosts him for illegally entering the rail yard. In his dazed state, Sullivan hits the man with a rock, earning himself a six-year sentence of hard labor in a work camp. He gradually regains his memory. In the camp, he attends a showing of Walt Disney's 1934 Playful Pluto cartoon, a rare treat for the prisoners, and is surprised to find himself laughing along with them.
Unable to convince anybody either that he is Sullivan or communicate with the outside world, he comes up with a solution: after learning of his unsolved "killing" on the front page of an old newspaper, he confesses to being the murderer. When his picture makes the front page, he is recognized and released. His "widow" has married his business manager, meaning she will have to give him a divorce or be charged with bigamy. Sullivan's boss finally tells him he can make O Brother, Where Art Thou? Sullivan confesses he has changed his mind; he now wants to continue making comedies, having seen firsthand the joy they bring to the downtrodden.
