Lewis plays a washed-up German circus clown named Helmut Doork during the beginning of World War II and the Holocaust. Although he was once a famous performer who toured America and Europe with the Ringling Brothers, Doork is now past his prime and receives little respect. After Doork causes an accident during a show, the head clown convinces the circus owner to demote Doork. Upon returning home, Doork confides his problems to his wife Ada, and she encourages him to stand up for himself. Helmut overhears the circus owner agreeing to fire him after the head clown issues an ultimatum. Helmut is distraught. He is arrested later by the Gestapo for ranting about Germany and drunkenly mocking Adolf Hitler in a bar. Following an interrogation at the Gestapo headquarters, he is imprisoned in a Nazi camp for political prisoners. For the next three to four years, he remains there while hoping for a trial and a chance to plead his case.
He tries to maintain his status among the other inmates by bragging about what a famous performer he once was. His only friend in prison is a good-hearted German named Johann Keltner, whose reason for being interned is never fully revealed but is implied to be his outspoken opposition to the Nazis. The camp receives a large group of Jewish prisoners, including several children. The other prisoners goad Doork into performing for them, but he does not realize he actually is not very good. The other prisoners beat him up and leave him in the courtyard to sulk about his predicament. He sees a group of Jewish children laughing at him from the other side of the camp, where the Jewish prisoners are being kept away from everyone else. Delighted to be appreciated again, Helmut performs for them and gains an audience for a while, until the new prison commandant orders that he stop.
Helmut learns that fraternizing with Jewish prisoners is strictly forbidden. Unable to leave the children in a state of unhappiness, he continues to perform for them. The SS guards break up one of his performances; they knock him unconscious and warn the children away from the barbed-wire fence. Horrified, Keltner fights off one of the guards, but he is quickly cornered and beaten to death. Doork is placed in solitary confinement. Seeing a use for him, the commandant assigns him to help load Jewish children on trains leading out of the internment camp, with the promise his case will be reviewed. By a twist of fate, he ends up accidentally accompanying the children on a boxcar train to Auschwitz, and he is eventually used, in Pied Piper fashion, to help lead the Jewish children to their deaths in the gas chamber.
Knowing the fear the children will feel, he begs to be allowed to spend the last few moments with them. Leading them to the "showers," he becomes increasingly dependent on a miracle, but there is none. He is so filled with remorse that he remains with them. As the children laugh at his antics, the film ends.

Question: Why did the prisoners beat up Doork?
Answer: Because his performance was not funny.
Alternative answer: because he performed for the Jewish prisoners and it turned out he wasn't very good