When a group of electrical workers investigates a bizarre power source in an abandoned Chicago building, they inadvertently discover a deserted laboratory. Inside appears to be a defunct nuclear power core, but its accidental activation suddenly opens a portal to a parallel universe. Suddenly they are trapped in a maddening mirrorworld where savage, cannibalistic beings with spider appendages stalk and swarm. Desperate and terrified, the dwindling band of survivors must fight back with primitive weapons against the growing storm of spider-people and their monstrous queen!