In the 1750s, Joseph Curwen (Vincent Price) is burned to death for being a warlock. He promises to return and get revenge on the descendants of his killers. 110 years later, Curwen's great grandson, Charles Dexter Ward (also Vincent Price), has inherited the family mansion. Charles and his wife Ann (Debra Paget) are met with hostility, as the townsfolk try to drive them away. Since Curwen's curse the town has been plagued with many deformed abnormal births.
At the mansion, Charles is taken by a portrait of Curwen that looks just like Charles. Curwen's spirit begins to take over Charles. They are surprised that the mansion is clean and prepared for them. Simon (Lon Chaney) says he was hired by Charles's lawyer as caretaker to prepare for his arrival. Really, Simon was Curwen's acolyte who has remained alive by black magic, awaiting Curwen's revival.
Charles & Simon dig up Curwen's mistress and revive the corpse. Ann is frightened by the changes in Charles. Charles secretly burns to death the heirs of 2 of his killers. The townspeople storm the mansion, and burn it down. When Curwen's portrait is thrown in the fire, it seems like Charles is free of outside control. However, Charles's final comments imply Curwen has taken over.
Thanks Joseph C!