Percival Glyde is murdered in his sleep with a wooden spike that is hammered into his skull. His killer (Tod Slaughter) steals his identity and moves into Glyde's London mansion. The family lawyer who has not seen the real Percival since he was a boy informs the madman of Glyde's arranged marriage to the beautiful heiress Laurie Fairlie. Greed and perversion drive this lunatic to the brutal killing of anyone who attempts to unravel his secret identity.