At a dig in rural Mexico, a British industrialist accidentally unleashes an ancient evil: a severed hand, possessed by a vengeful demon, that attacks, kills and takes over the hand and mind of anyone who interferes with its ruthless quest for violence. Determined to stop the bloodshed, the wife of the industrialist (Samantha Eggar) joins forces with a renegade priest (Stuart Whitman), but will they be able to conquer the evil hand before the forces of hell overtake them?