MONSTROSITY

In an atomic-powered laboratory beneath the mansion of the elderly, unpleasant, and very rich Mrs. Hettie March, Dr. Otto Frank is experimenting with brain transplantation. Things are not going very well, though, as all Dr. Frank has succeeded in creating so far is Hans, a snarling man-beast with a dog's brain, and the "Walking Corpse" – a pretty young woman who wanders about the lab with a brain-dead glassy-eyed stare. Dr. Frank's goal is to carry out the wishes of Mrs. March and transplant her brain into the head of a beautiful younger woman.

To that end, Mrs. March advertises for domestic help and hires Nina Rhodes from Austria, Bea Mullins from England, and Anita Gonzales from Mexico. Mrs. March plans to pick out the best-looking of the three and use her as a body donor so that she will become one of the richest and most beautiful young women in the world. She rejects Anita because the birthmark on her back makes her imperfect and chooses the curvaceous blonde Bea instead.

Anita is turned over to Dr. Frank for experimentation, and he transplants the brain of Xerxes the cat into her head. Anita immediately takes on the aspects of cat behavior: purring, hissing, eating mice, etc. Neither Nina nor Bea know what has happened to Anita, and when Bea comes across her, she scratches out one of Bea's eyes. Nina finds Anita on the roof of the mansion and attempts to get her down, but Anita loses her footing and falls to her death.

Because of Bea's injury, Nina becomes by default the choice for Mrs. March's new body. However, Dr. Frank, wanting to take full control of his work, instead transplants Mrs. March's brain into Xerxes. Now a cat, Mrs. March is quite unhappy about this unexpected development, and after scratching Dr. Frank's hand in anger, locks him inside his atomic-powered experimental chamber when he enters it. Xerxes/Mrs. March then starts the chamber, which quickly reduces Dr. Frank to a skeleton, and also begins the chain reaction in the atomic pile below the lab that will cause it to explode, destroying all evidence of the lab and burning the mansion to the ground.

A half-blind Bea stumbles into the lab to rescue Nina. But as the lab starts coming apart, Bea is killed when a piece of machinery falls on her. Nina flees into the night, unaware that following silently behind her is Xerxes/Mrs. March, waiting for a chance to someday, somehow claim Nina's body as her own.

Mrs. March's brain is transplanted into a cat, Dr. Frank is killed by an atomic chamber, the mansion is destroyed, and Nina escapes while Mrs. March, now in a cat's body, follows her.

The ending subverts the villain's quest for eternal youth by trapping Mrs. March in a cat's body, making her the ultimate victim of her own hubris. Dr. Frank's demise and the destruction of the laboratory symbolize the catastrophic consequences of playing god with science, while Nina's escape hints that the threat may not be over as Mrs. March, now a cat, continues to pursue her goal.