Description
After nurse Jane Marvin (Beverly Garland) is administered the drug sodium pentothal by psychiatrists Erik Lorimer (Bennett) and Wayne McGregor (Douglas Kennedy), she recalls a series of 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. 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 at the rail station, she notices a large crate, marked as containing radioactive cobalt, and meets Manon (Chaney Jr.), a handyman at the Cypresses, when he comes to pick up the crate. She asks him to drive her there and he obliges. As they proceed deeper in the swamps, Joyce is horrified when Manon tries to run over an alligator and then exhibits the hook where a gator bit off his hand, explaining his hatred for the reptiles. At the plantation, Joyce introduces herself to Lavinia Hawthorne (Frieda Inescort), the Cypresses\' stern mistress. When Joyce suggests that Paul once lived at the plantation, Lavinia calls her a liar and tries to have her thrown out. However, when her manservant Toby (Vince Townsend Jr.) points out that 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, in a drunken craze, Manon 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 Joyce\'s 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 Paul\'s 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.
Meanwhile, at the house, 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 Lavinia\'s 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, thinking that Joyce has gone, Paul 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, Manon rescues and carries her to his shack. After trying to get her to strip, Manon assaults her. When Joyce screams and tries to resist, Manon angrily knocks her unconscious. An outraged, reptilian-looking Paul then bursts in and fights Manon. After a struggle, Paul manages to incapacitate Manon and takes Joyce back to the house. Manon recovers and screams out in rage into the storm, vowing to kill Paul just like he would kill any alligator no matter what. 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 increasingly take on reptilian traits. 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 Paul\'s 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, Manon bursts into the lab and destroys the control panel, shooting powerful rays at Paul that transform him into a bipedal, reptilian monster with an alligator-like head. After trying to attack Manon, Paul looks on as Manon\'s hook gets caught on some cords and is electrocuted while trying to kill Paul. Confused, Paul stumbles over to the other room and tries to communicate, but his voice has been replaced with a reptilian 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 Manon\'s body, self-destructs and destroys the lab. Scrambling away from his wife, Paul is attacked by an alligator and wrestles it while Joyce screams at the sight. Managing to fight off the reptile and hurl it away, Paul stumbles into quicksand and slowly sinks out of sight to the sound of Joyce\'s shrieks, seemingly meeting his demise.
Back in the present, the psychiatrists review the tapes of Joyce\'s 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.
