For treating a wounded revolutionary, respected surgeon, Dr. Charles Gaudet (Boris Karloff) is sentenced to life imprisonment to the infamous French penal colony on Devil's Island. It isn't long before he speaks out against the inhuman conditions and incurs the anger of the brutal prison commander, Colonel Armand Lucien (James Stephenson). But when Lucien's daughter Collette receives life-threatening wounds in an accident, the only person on Devils Island who can save her, is Gaudet.