On New York's Lower East Side, Mama Teresa Lorenzo labors in her spaghetti restaurant, determined to keep her young son Joe honest. When Joe and his friend Nick get into trouble for slugging a railroad detective, Mama saves the boys from the reformatory by promising to discipline Joe and adopt the homeless Nick. While Nick earns straight A's in school and continues on to college, Joe turns to gambling and crime. Joe finances Nick's education and leads his family to believe that he is running a ranch in California, but is actually serving a prison term in San Quentin. Upon finishing his sentence, Joe returns to New York to attend Nick's college graduation and brings his girl friend, Laurie Romayne, who is wanted on a forgery charge, with him. In New York, Laurie, touched by Mama's kindness and concern, begins to help with the household chores and discovers that she enjoys the honest life. Meanwhile, Joe plots revenge on Scarfi and Cy Turner, the two gangsters he blames for sending him to Quentin. Joe informs the police of a robbery that the two are planning, but Turner escapes the police trap. When Scarfi is sent to the electric chair for shooting a policeman, Turner vows to take Joe's life in revenge. To avoid Turner's thugs, Joe leaves town, but Laurie decides to stay with Mama. In Joe's absence, Laurie gets a job, and she and Nick fall in love and decide to marry. In Mexico, Joe learns of their plans and returns to stop the wedding. He threatens to expose Laurie's past unless she gives Nick up, but Mama, learning of Joe's treachery, renounces him as her son. Joe relents, and after delivering Laurie to the church, he eludes the clutches of Turner's thugs by slugging a policeman and getting arrested.