Tired of the crime overrunning the streets of Boston, Irish Catholic twin brothers Conner and Murphy are inspired by their faith to cleanse their hometown of evil with their own brand of zealous vigilante justice. As they hunt down and kill one notorious gangster after another, they become controversial folk heroes in the community. But Paul Smecker, an eccentric FBI agent, is fast closing in on their blood-soaked trail.

In 1839, the slave ship Amistad set sail from Cuba to America. During the long trip, Cinque leads the slaves in an unprecedented uprising. They are then held prisoner in Connecticut, and their release becomes the subject of heated debate. Freed slave Theodore Joadson wants Cinque and the others exonerated and recruits property lawyer Roger Baldwin to help his case. Eventually, John Quincy Adams also becomes an ally.