- "Weird Monster Escapes! Terror Siezes City!...a woman's beauty the lure for his dangerous desires!"
- ―Revenge of the Creature tagline
In the Amazon a ship navigates down the river. The ship is revealed to be manned Lucas who is bringing two men, George Johnson and Joe Hayes to the The Black Lagoon. Joe wishes to capture the Creature and bring him to Ocean Harbor Oceanarium.
When they arrive at the lagoon Joe uses a diving suit to secure a net at the entrance to the lagoon to prevent the Creature from escaping. While he does this the Creature attacks him, until the men on the boat drive him away with gunfire.
The next day, the men set up explosives in the lagoon. When the detonate them, the Creature is stunned and floats unconscious to the surface, allowing for his capture.
At an Institute in Florida, Professor Clete Furguson is encouraged to go to the Aquarium to study the Creature. At Ocean Harbor, the Creature is transferred into a holding tank so that studies may begin. Joe works to revive the Creature, who has been in a coma ever since his capture by walking him through the tank so water passes through his gills. Helen Dobson is overseeing the study, and is interviewed by a radio man. After two hours of the treatment, the Creature awakens and attacks. Two men are badly injured before he is finally brought under control.
The Creature is then put into a main tank where the public can see him. He is chained by one leg to the bottom of this tank.
Furguson meets Helen, and invites her to diner, although they are interrupted by Joe, who is also interested in Helen, but she ultimately favors Furguson. Clete and Helen begin experiments on the Gill-man using vocal commands. They enter the tank armed with a shock pole to condition him into expecting pain whenever he disobeys a command.
They then lower a portion of food that is injected with drugs, which makes the Gill-man go to sleep, which enables Furguson to draw blood samples and study his brain activity. The blood tests show unexpected results which indicate the Creature is more man than animal.
Helen readies for a shower, unaware the Gill-man Chris attacks the Creature.
- John Agar as Professor Clete Furguson
- Lori Nelson as Helen Dobson
- John Bromfield as Joe Hayes
- Nestor Paiva as Lucas
- as Jackson Foster
- as Lou Gibson
- Robert Williams as George Johnson
- Tom Hennesy as Gill-man (land)
- Rico Browning as Gill-man (water)