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Widow Julia Endicott rewrites her will, leaving her fortune to her alcoholic nephew Herbert, on the condition that he move into her estate, instead of her son Phillip, who is mentally deficient but physically powerful.  Later, Herbert's greedy wife Laura cajoles him to murder Julia, but Phillip, who is known to be bloodthirsty, is arrested for the crime.  Having seen a demonstration of Phillip's strength, police lieutenant Valcour believes he is innocent, since he would have broken Julia's neck, not strangled her.

Laura's lover, Thomas Hollander, strangles Herbert, who happens to be his best friend, after Laura lies that he has brutalized her.  Herbert survives, however, and unaware of Tom's involvement in the matter, Valcour calls Tom to Herbert's bedside.  When Herbert begins to revive, Tom tries to stab him but is stopped by a policeman.

In the meantime, Laura, presumed to be asleep from a sedative given to her for shock, appears as Julia risen from the dead and shocks Herbert to death.  Later, Phillip escapes from jail at Laura's suggestion and kills Tom in front of her, then kidnaps her and takes her to Julia's crypt.  In a secret passageway, Valcour finds Julia's body and a plaster of paris mask of her face, from which he gets Laura's fingerprints.

Struggling with Phillip in the crypt, Laura presses Julia's casket alarm, which she had installed before she died out of fear that she might be buried alive.  Valcour comes to Laura's rescue, but despite her amorous advances, arrests her for Herbert's murder, since she frightened him to death with the mask of Julia.