In 1920s Ireland, young doctor Damien O'Donovan joins his brother Teddy in the Irish Republican Army to fight for independence from Britain. After a series of events, including witnessing the execution of his friend and being sworn into Teddy's IRA brigade, Damien becomes embroiled in the guerrilla warfare of the Irish War of Independence. As tensions rise during the Irish Civil War, Damien is torn between his loyalty to the cause and his own moral principles, ultimately leading to a tragic confrontation with his brother.