In 1973, the first manned expedition to Mars is marooned; by the time a rescue mission arrives, there is only one survivor: the leader, Col. Edward Carruthers, who appears to have murdered the others! According to Carruthers, an unknown life form killed his comrades during a sandstorm. But the skeptical rescuers little suspect that "it" has stowed away for the voyage back to Earth...
An old lighthouse keeper who lives with his daughter secretly keeps a prehistoric fish-man by feeding it scraps and fish. One day he misses the feeding and all hell breaks loose.
A scientific expedition searching for fossils along the Amazon River discover a prehistoric Gill-Man in the legendary Black Lagoon. The explorers capture the mysterious creature, but it breaks free. The Gill-Man returns to kidnap the lovely Kay, fiancée of one of the expedition, with whom it has fallen in love.
Men capture the creature from the Black Lagoon and make him an aquarium attraction, from which he escapes.
The third film in The "Creature From The Black Lagoon" franchise sees the Gill Man turned into an air-breather by a mad scientist.