A group of animal activists, who call themselves LD 50, break into an animal research facility, when Gary gets caught in a bear trap. Unable to free Gary, the rest of the group flees, leaving Gary to take the blame. A year later, the group has since disbanded until an encrypted e-mail from Gary arrives asking for help. Danny, who has been visiting Gary in prison, tells the group that Gary has traded his body for experiments in exchange for a reduced sentence.

The group, still stricken by guilt one year later, eagerly reunites to rescue Gary. They also pick up two new recruits — a stoner and an ex-Marine. At the remote lab where Gary is being kept, the group discovers the place abandoned, and soon finds themselves locked in a subterranean level full of labyrinthine hallways and experiment chambers. They also discover that a powerful electrical force is stalking them, and it has full control of the complex. The force plays havoc with the would-be rescuers, turning their righteous cause into a death trap. They must work together to outsmart and defeat the unseen evil.