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American burlesque performer Steve Martin offers to play a song for his audience, if they agree to sing along. Only one person does sing, a young boy named Asa Yoelson. Steve is bowled over by the boy's voice, but Asa realizes he should be singing at the synagogue with his father, Cantor Yoelson. Asa arrives late, and is later reprimanded by his strict father. Asa is reluctant to explain where he was, but Steve Martin visits the Yoelsons' home. He explains that he heard Asa sing at the burlesque house, and that he wants Asa to be part of his act. Papa Yoelson refuses to consider it.
Asa is determined to be in the act, and runs away to Baltimore, where he is taken to a home for boys. The kindly superintendent, Father McGee, finds Steve Martin and notifies Asa's parents. When they appear, Asa tells them that he will keep running away until they allow him to go into show business. Asa's mother believes that it would be better to give Asa what he wants than have him running away all the time.
On stage, Asa gets bored with singing songs the same way all the time, and begins to improvise. When his voice suddenly breaks, he starts whistling instead, but is unhappy and wants to go home. Steve says that they can work on stage together - previously Asa has only stood in the audience. Asa changes his mind, and his name: he performs as Al Jolson.
At a show, blackface entertainer Tom Baron passes out drunk, and Al goes on in his place. Two theatrical entrepreneurs, Oscar Hammerstein and Lew Dockstader, are in the audience. Dockstader realizes that it was really Al who was on stage, and hires him join his minstrel show. One night, Jolson is out walking when he hears the new, exciting jazz music; he enjoys it so much that he forgets that he has a show that night. Dockstader fires him.

Al Jolson