This movie employs a premise similar to The Undead — transferring the consciousness of a past person into the body of another. Said subject will then speak as if they have the memories of this other person. This is being performed by Dr. Carlo Lombardi, a slimy, repulsive stage performer with hypnotic mojo and a chip on his shoulder. Lombardi happens to be keeping a woman, Andrea, against her will as the star of his "past-life-regression" act. On the side, he's trolling the local police about a series of mysterious murders happening around the carnival as he predicts each one. The lead detective can tell he's guilty but he's always got an ironclad alibi.
Timothy Chappel, a slumming businessman who hears about Lombardi's predictions, decides to make him into the next big thing. Predicting each of the continuing murders works wonders for publicity. It turns out that Lombardi uses Andrea to summon the titular She Creature (supposedly a previous incarnation of her, from prehistoric times!) to emerge from the ocean and start killing people. It's up to the newly minted Love Interest of Lombardi's thrall, a calm "psychical" researcher named Ted Erickson, to save the day. Can he prevail?
The She Creature contains examples of the following tropes:
- Abhorrent Admirer: Dorothy Chappel spends most of the film fending off an alcoholic man while trying to win Ted's affections. At the end, he stops drinking very quickly and wins her affections once she decides to give up on Ted.
- Lombardi is also this to Andrea. Even though she is enslaved to him, he can't make her love him.
- Agent Scully: Professor Anderson, the scientist who accompanies Dr. Erickson to a demonstration of Lombardi's powers. It's one thing to have curtains or windows close, but when an invisible force removes your glasses from your face, to dismiss it as "absolutely meaningless" without further investigation is scientifically unsound.
- Alternate Company Equivalent: Wonder Woman's foe, Dr. Psycho, used a similar plot in his original appearances.
- And You Thought It Was a Game: Throughout the whole movie all the others characters think that Lombardi is just a creepy, con-artist who is keeping Andrea enslaved, and all his magic tricks are just tricks, and that he might be committing the murders himself. Turns out that he does have psychic powers and a monster he summoned was committing the murders all along.Lombardi: Do you believe now!? Kill him!
- As You Know: In the form of actual "maid and butler" dialogue as two Ethnic Menial Labor servants comment on everything going on at a party.
- Betty and Veronica: Mr. Chappel's daughter Dorothy starts the film seeing Ted, but rapidly loses his attention to Andrea.
- Hell Hound: King the dog briefly becomes this after being hypnotized by Lombardi.
- Heroic Willpower: Andrea begins showing resistance to Lombardi's hypnosis near the end.
- Hoist by His Own Petard: Lombardi should've known better than to try to have the monster kill her current incarnation's love interest.
- I Love You Because I Can't Control You: For all the power Lombardi has over Andrea the one thing he can't do is make her love him, so much so that she instantly snaps out of his control when he tries to make a move on her. This both infuriates him and makes him want her even more.
- Non-Mammal Mammaries: Despite being some amalgamation of fish and reptile, the She-Creature has a pair of highly-visible lumps on her upper chest.
- That Poor Plant: Dorothy's alcoholic Abhorrent Admirer pours out the contents of his drink on the landscaping as a sign of good faith to her after she was formally dumped by Dr. Ted.
- The Thing That Would Not Leave: Lombardi moves in to Mr. Chappel's house as soon as their partnership begins and immediately starts abusing his host's hospitality. Timothy eventually orders Lombardi to leave; the hypnotist doesn't take it well.
- Villain's Dying Grace: After the She-Creature fatally wounds Lombardi, he frees Andrea from her trance with his dying breath, and even gives her one last command to make her immune to any attempts at hypnosis in the future to boot!
- Who's Laughing Now?: Lombardi's entire motivation. He tries to kill people who wronged or humiliated him in some way, and goes out of his way to taunt both the respectable scientist hero and the skeptical police detective with the evidence of his hypnotic powers.