Told entirely in flashback, Jane Marvin (Beverly Garland) remembers her troubled past for two psychiatrists (Bruce Bennett and Douglas Kennedy) during an extended hypnosis session while under the influence of Sodium Pentathol.
It turns out her real name is Joyce Webster and her husband Paul (Richard Crane) disappeared suddenly from a train while they were on their honeymoon.
Joyce spends years searching for him, finally ending up at a mysterious plantation called The Cypresses – run by the tyrannical Mrs Lavinia Hawthorne (Frieda Inescort) – in the bayous of Louisiana.
She is accompanied by her unhinged hired hand – a sleazy, one-armed, alcoholic gator hating swamper called Manon (Lon Chaney Jr), the local “swamp doctor” Dr Mark Sinclair (George Macready), and an assortment of other household helpers.
Everyone keeps telling Joyce to leave, but she stays and eventually finds her missing husband – who has been partially turned into an alligator!
It seems that Dr Sinclair has been trying to help accident victims with some tissue and limb regeneration research using alligator extract, and while the victims recover, there are some pretty nasty side-effects . . .
Paul Webster is now scaly and has a deep, rumbling voice, as a result of receiving too much alligator hormone.
Sinclair believes that he can cure Paul through “massive radiation from a cobalt bomb” – but adds that the exposure can be no longer than 30 seconds (“I determined that with my test alligator”!)
At the critical moment during the treatment, Manon bursts in, knocks out the doctor, and electrocutes himself on the space-age equipment – but not before Paul has been turned into a true “gator-man”, with a big alligator head and a scaly chest. He is, however, still wearing his neatly pressed trousers and belt!
Paul runs into the swamp, followed by his wife – who still loves him even in his reptilian condition – and a monstrous explosion destroys The Cypresses, The gator-man disappears in a convenient quicksand pit leaving Joyce to sit screaming in the middle of the swamp.
We return to the two psychiatrists, who have listened incredulously to the whole story and now decide to do nothing at all about the situation. The end.
20th Century-Fox commissioned the film because they needed a low-budget monster movie in CinemaScope format to play on the bottom of a double bill with Return of the Fly (1959), the sequel to The Fly (1958).
Joyce Webster/Jane Marvin
Dr Eric Lorimer
Lon Chaney Jr
Dr Mark Sinclair
Mrs Lavinia Hawthorne
Dr Wayne MacGregor
Vince Townsend Jr
Roy Del Ruth