In Boston, two Irish-American brothers, Connor and Murphy McManus, find themselves in a self-defense situation which results in the death of two Russian mobsters. This incident sparks a religiously fueled epiphany in them, driving the conviction that they have been chosen by God to eradicate evil men from the world. The brothers decide to embrace this calling fervently, setting out to rid the city of criminals in a vigilante mission. Their actions are both violent and methodical, adhering to a moral code that justifies their killings as a divine mandate. With each act, they leave behind a signature prayer, becoming folk heroes in the public eye, even as their methods raise serious ethical questions.

As the brothers continue their crusade, they attract the attention of an eccentric and highly skilled FBI agent, who is both appalled by the vigilantes’ disregard for the law and intrigued by their effectiveness. The agent embarks on a meticulous quest to track them down, delving into a murky world where the line between good and evil blurs. The brothers, meanwhile, expand their mission, targeting the city’s underworld with increasing boldness. Their journey brings them face-to-face with Boston’s most powerful crime figures, setting the stage for a conflict that has profound implications for their mission, their lives, and the fabric of the city itself.