Karloff (in a typically fine performance) plays a French brain surgeon who treats an injured escapee from Devil's Island. Karloff is arrested and sentenced to serve ten years on the island. The island is run by a brutal commandant, Stephenson, who treats the inmates worse than animals.
Angered by the brutality and corruption he witnesses, Karloff leads the inmates in an attempted revolt, but fails. For his insolence, he and his confederates are sentenced to death. Luckily, they are given a reprieve when the daughter of the commandant is injured in an accident and Stephenson's
wife, Harrigan, forces her husband to suspend the death sentences if Karloff will operate ...