A never-before-seen woodsman mysteriously appears aboard a submarine that's been trapped deep under water for months with an unstable cargo. As the terrified crew make their way through the corridors of the doomed vessel, they find themselves on a voyage into the origins of their darkest fears.

Walrus-like warden, Sven "Swede" Sorenson, a cross between Bluto and Wimpy, runs the prison, murders convicts who escape, and has the FBI on his trail in the form of agent Karen Polarski, the daughter of the town's corrupt judge. Swede's twins tell their father they're pregnant (they aren't), so he pushes their dim boyfriends, Bud and Larry, into shotgun marriages. He also turns his sons-in-law into slave labor, so Bud hatches an escape plan: to rob a train carrying old bills to the mint for burning. Larry's his reluctant accomplice. When Bud is captured and railroaded into Swede's jail, his death looks certain, until he hatches yet another plan that requires Larry's help.

A weathered detective teams up with a young female archaeologist to unravel the mysterious death of...