During the 1860s, Tom Edison (Mickey Rooney) is a precocious boy with a penchant for mischief. After setting off a smoke bomb, he is expelled from his school to the dismay of his father, Samuel (George Bancroft). However, Tom's mother, Nancy (Fay Bainter), knows that he is incredibly gifted. After Tom rescues a young boy from an oncoming train, the boy's father, Mr. McCarney (J.M. Kerrigan), offers him a job in a telegraph office, where's he's finally given a chance to prove himself.