SPOILERS!!!!
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. Helmut is arrested by the Gestapo for ranting about Germany and drunkenly mocking Adolf Hitler in a bar. After 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 keep his bravado up 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 others goad Doork into performing for them, but he does not realize he is, in fact, terrible. Frustrated, they beat him up and leave him in the courtyard to sulk about his predicament. Suddenly, 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. Feeling delighted to be appreciated again, Helmut performs for them and gains quite an audience for a while, until the new prison commandant orders that he must be stopped.
After learning that fraternizing with Jewish prisoners is strictly forbidden, Helmut is unable to leave the children in a state of unhappiness and begins performing again. The SS guards break up his latest performance; they knock him unconscious and start beating 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. Meanwhile, 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 while being led to their deaths, he begs to be allowed to be the one to spend the last few moments with them. Leading them to the "showers", he becomes increasingly dependent on a miracle, only to learn there is none. After all the children go into the chamber, he is so filled with remorse that he goes into the room himself to entertain them. As the children laugh at his antics, the movie ends