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After she is administered the drug pentothal by psychiatrists Dr. Erik Lorimer (Bruce Bennett) and Dr. Wayne McGregor (Douglas Kennedy), nurse Jane Marvin (Beverly Garland) recalls a series events from her forgotten past when she was known as Joyce Webster.
Joyce has just married a young man named Paul Webster (Richard Crane). Aboard their honeymoon train, Paul receives a telegram and, in a panic, immediately leaves the train to make a phone call. When the train pulls out, Paul is missing, having vanished without a word to Joyce. Throughout the following months, Joyce employs private detectives and conducts her own search for her husband to no avail, until one day, she discovers the address of the Cypresses Plantation that Paul entered on his college enrollment forms.
Joyce takes the next train to the desolate whistle-stop town of Bayou Landing in the heart of Louisiana swamp country. While waiting forlornly at the rail station, she notices a large crate marked to be containing radioactive cobalt. Surmising no one would leave such cargo alone long, she stays by it and meets Mannon (Lon Chaney Jr.), a handyman at the Cypresses who came to pick up the cobalt. She asks him to drive her there and he obliges. As they proceed deeper in the swamps, Joyce is horrified when Mannon tries to run over an alligator and then exhibits the hook where a gator bit off his hand. At the plantation, Joyce introduces herself to Lavinia Hawthorne (Frieda Inescort), the Cypressesâ stern mistress. When Joyce suggests that Paul once lived at the plantation, Lavinia bristles and calls her a liar and tries to have her thrown out. However, when her manservant Tobee (Vince Townsend Jr.) points out Joyce has missed the last train back to town, Lavinia reluctantly invites her to stay the night under the proviso that she not leave her room.
That night, Mannon, in a drunken craze, is in the swamps attempting to shoot several alligators. Joyce is disquieted by the sound of gunshots, but when she tries to open the door to her room, she discovers it is locked. When the maid Lou Ann (Ruby Goodwin) delivers Joyceâs dinner tray, she warns that the house is deeply troubled and advises her to leave as soon as possible. Later, Lavinia notifies Mark Sinclair (George Macready), a self proclaimed "Swamp Doctor" who operates a clinic on the plantation, that Paulâs wife is there. At the clinic, Mark administers an injection to an agitated patient who is swathed in bandages. Soon after, Lavinia arrives to confer about how to deal with Joyce.
At the house, meanwhile, Joyce hears the strings of a piano and slips out of her room to investigate. As she descends the stairs, she sees a man in a trench coat, his face in shadows, seated at the piano and fails to recognize the shadowy figure as mutated Paul. When Joyce enters the room, Paul flees, leaving behind a trail of muddy, clawed footprints. Paul, his face terribly disfigured, stops Laviniaâs car and in a distorted voice, insists that Joyce leave as soon as possible. The next morning, Mark comes to the house to question Joyce, and sensing that he is withholding information about Paul, she refuses to leave. Later that day when Joyce demands that Lavinia tell her what she did to Paul, the older woman breaks down and confesses that Paul is her son.
That night, as a storm rages, Paul, thinking that Joyce has gone, returns to the house. When Joyce sees him, he runs away and she follows him into the swamps. After being menaced by several alligators and a giant snake blocking her path, Joyce screams, and Mannon appears and carries her to his shack. After trying to get her to strip, Joyce screams and he assaults her. When Joyce tries to resist, Mannon smacks her unconscious. An outraged, reptilian-looking Paul then bursts in and fights Mannon. After a struggle Paul manages to incapacitate Mannon and takes Joyce back to the house. Mannon recovers and screams out in rage into the storm, vowing to kill Paul. Back at the house, Lou Ann is caring for Joyce as Lavinia confronts her son. After his mother insists that Joyce be told the truth, Paul presses Mark to give him an untested cobalt treatment in hopes of curing his condition. Mark reluctantly agrees to give him the treatment the following evening after Joyce has been informed of the situation.
The next morning, Mark summons Joyce to his lab and tells her about his experiments with reptilian hormones that are capable of regenerating limbs. He continues that after Paul was horribly mangled in a plane crash, Mark administered the serum to him and several other accident victims. The treatment appeared to be a great success, until his patients began to take on reptilian traits at increasing rates. Mark explains that after Paul received the telegram notifying him that his tests were positive, he hurriedly left the train and came home in hopes of reversing his condition. When Joyce learns of Paulâs scheduled radical cobalt treatment, she insists on being present.
That night, Paul encounters Joyce at the clinic and turns away from her in shame. After seeing Joyce clasping her son's hands and reassuring him of her love, Lavinia apologizes to her for her brusqueness. As Paul climbs onto the table and Mark aims the ray at him, Mannon bursts into the lab and destroys the control panel, shooting powerful rays at Paul that transform him into bipedal, reptilian monster with an alligator like head. After trying to attack Mannon, Paul looks on as Mannon's hook is caught on some cords and is electrocuted to death while trying to attack Paul. Confused, Paul stumbles over to the other room and tries to communicate, but his voice has been replaced with a crocodilian snarl. Hearing his wife and mother scream in horror, Paul flees into the swamps and sadly peering into the water, sees his reflection. Joyce scrambles after him, as the cobalt machine, short circuiting due to Mannon's body; self-destructs and destroys the lab. Scrambling away from his wife, Paul is attacked by and wrestles an alligator while Joyce screams at the sight. Managing to fight off and hurling the reptile away, Paul stumbles into quicksand and slowly sinks out of sight to the sound of Joyceâs shrieks.
Back in the present, the psychiatrists review the tapes of Joyceâs ordeal and, concluding that her amnesia has allowed her to suppress the horror and resume a normal life, they decide not to tell her about her life as Joyce Webster.
The film is set in the Southern United States and is one of many monster B-movies released in the era.
What is the name of Paul Webster's wife?
Joyce