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.

Detective Brighton investigates a series of unusually gruesome murders and is soon caught in a web of intrigue involving a mad scientist, a beautiful woman, a power mad politician, and one very ferocious monster. Their secret lies in a mysterious formula which could unlock the secrets of immortality... and on a less positive note, also cause the mass mutation of all life on earth! The bodies pile up as everyone scrambles for possession of the formula. It culminates in a climactic showdown whose outcome will determine the fate of all mankind!