In 1921 Dublin, the IRA battles the "Black & Tans," special British forces given to harsh measures. Irish-American medical student Kerry O'Shea hopes to stay aloof, but saving a wounded friend gets him outlawed, and inexorably drawn into the rebel organization by his former professor Sean Lenihan, who has "shaken hands with the devil" and begun to think of fighting as an end in itself. Complications arise when Kerry falls for a beautiful English hostage, and the British offer a peace treaty that is not enough to satisfy Lenihan.