The story takes place in Chicago, an area full of violence in the 1930s in the United States. The Irish-born Rooneyplayedis the leader of a gang, where he has his own "turf" and two capable assistants: his son Kunalplayedand his adopted son. Sullivan is a formidable professional killer; but at the same time he values his family very much, he is loyal to his wife and two sons, never smokes or drinks, and his family life is very regular. Over the years he has struggled to maintain a balance between the roles of killer and husband and father.
Although Sullivan’s two sons, Michael and Peter, did not know what their father was doing, they always regarded him as their heroes and admired them very much. Little Michael is 12 years old, and he is gradually sensible. He really wants to know his father's occupation. So one day when his father and Kunar went out to work, he secretly hid in the car. Soon after, little Michael witnessed a murder, and his father was the killer.
People in the gang worry that little Michael will leak everything they see. Sullivan only said one thing: He is my son. However, this does not reassure others. Little Michael has not had time to understand the real world and his father. His mother and younger brother have been killed, and he and his father were the targets of this killing.
The father and son began to flee. Although his son begged him not to have any more violence, Sullivan decided to avenge Rooney. Rooney and Kunar both went into hiding, Sullivan decided to attack their business strongholds one by one until they came out to fight.
