In 1931, during the Great Depression, Michael Sullivan, Sr. is an enforcer for Irish mob boss John Rooney in Rock Island, Illinois. Rooney raised the orphan Sullivan and loves him more than his own biological son, Connor. Rooney sends Connor and Sullivan to meet with disgruntled associate Finn McGovern, but Connor shoots McGovern, resulting in Sullivan gunning down McGovern’s men. Sullivan’s twelve-year-old son Michael Jr. has hidden in his father’s car and witnesses the event. Despite Sullivan swearing his son to secrecy and Rooney pressuring Connor to apologize for the reckless action, Connor murders Sullivan’s wife Annie and younger son Peter. At the same time, he sends Sullivan to an ambush at a speakeasy. Sullivan realizes it’s a set-up, kills two men at the bar, and escapes. He goes to Chicago with his son to seek Al Capone, for work and to discover the location of Connor, who has gone into hiding.