Sexually abused by her brothers, Kate Barker runs away to become involved in bootlegging. She marries decent George Barker and gives birth to four sons, Herman, Arthur ("Doc"), Lloyd and Freddie. However, when George's law-abiding ways fail to provide for the family, "Ma" encourages her sons to commit crimes. Soon they become notorious criminals. FBI leader, J Edgar Hoover puts agent Melvin Purvis on the case. Meanwhile Alvin Karpis joins the gang. An attempted robbery leaves one Barker son, Herman, dead, and another Freddie, captured. Arthur Dunlop, a corrupt prison guard, helps Freddie escape and becomes Ma's lover. Dunlop plans a kidnapping that will net them $100,000, but it nearly goes wrong because of his incompetence. The gang kill him. They also kill another incompetent associate, a mob-doctor who messes up an attempt at plastic surgery. By this time Purvis is onto them. Lloyd and Arthur are arrested in Chicago, and Ma and Freddie are killed in a shootout in Florida.