Set during the Great Depression, the story unfolds around Michael Sullivan, a hitman for an Irish mob family in the Midwest, led by John Rooney. The deep bond between Sullivan and Rooney, however, extends beyond their business; Rooney is a surrogate father to Sullivan, having raised him since boyhood. The narrative takes a dark turn when Sullivan's oldest son, Michael Jr., stumbles upon his father's true profession after witnessing a brutal killing. This revelation shatters the boy's view of his father, setting them both on a harrowing journey that tests the limits of their relationship.

Fearing for his son's safety and seeking retribution, Sullivan embarks on a path of vengeance that pits him against his own criminal brotherhood and the treacherous Connor Rooney, John's real son, who harbors his deep-seated jealousy and ambitions. The ensuing conflict forces the Sullivans to flee, leading them down a perilous road marked by hitmen, betrayal, and the harsh realities of their chosen lives. As they navigate this dangerous underworld, the bond between father and son is both tested and solidified, uncovering truths about loyalty, redemption, and the unbreakable ties of family.