With nothing but their heritage in common, no one would have suspected that Irish-American officer of the peace Tom O'Meara (Harrison Ford) and Rory Devaney (Brad Pitt) - aka angry and bitter IRA terrorist Frankie McGuire - would come to know one another. But when McGuire arrives in New York on a terrorist mission to buy weapons, he takes on the false identity of Devaney, a young man seeking refuge from his country's troubles.
With the support of a friendly judge, McGuire moves into the O'Meara family home. O'Meara welcomes McGuire with open arms, unaware of his true identity. In the safe haven of the O'Meara household, the two men immediately form a bond. McGuire sees a strong and patient man, not unlike his father, who was gunned down by paramilitaries when he was just a child. O'Meara, a man with only daughters, feels pride in taking this troubled but charming young man under his wing.
However, McGuire is aware that his terrorist mission is calling while O'Meara, in the midst of a personal crisis, struggles with his conscience when his friend and partner Edwin Diaz asks him to help cover up a shooting.
Violence soon descends upon O'Meara's family home and he begins to realise that McGuire is not who he seems. McGuire must make a decision - will he choose O'Meara's promise of peace, or a lifetime of murder?