Description
A scientific expedition to a remote Mexican fishing community, led by Dr. Rick Torres (Kerwin Mathews) and Susan Lowry (Pier Angeli), discovers unhealthy amounts of radiation in the local waters. They find a small mutant octopus that can crawl on land, and Torres travels back to the States to present his findings, hoping to be granted more funding. Reception from the scientific establishment is lukewarm, so Torres makes a deal with Johnny Caruso, a circus owner who is interested in the bizarre mutation as a carny act. After their departure, a humanoid octopus, Octaman, attacks the camp and slaughters the remaining crew.
The scientists return to the camp in an RV a few days later and find it abandoned. Davido, a young Indian man from the nearby village, says that a local legend about a creature said to be half man and half sea serpent is true, and offers to take the scientists to the lake where it is purported to live. Meanwhile, Octaman kills some villagers. The next day, the scientists find another small mutant octopus, and Octaman has gone to the camp and killed a crew member and escaped. Johnny, witness to the attack, decides to capture the monster for his circus.
Octaman returns to the RV, but Lowry honks the horn to signal for help. The other scientists arrive and the monster flees. They go searching for it on the lake, and it pulls down another crew member out of their boat. When it reappears at the RV and captures Lowry, they blind it with their flashlights to stop it in its tracks, then light a ring of gasoline around it. The fire consumes enough oxygen that the monster suffocates and falls unconscious, and Lowry gets rescued. They finish the capture by tranquilizing it and trapping it under a net. In the morning, however, a thunderstorm brings rain which revives the Octaman and allows it to escape. It moves to seize Lowry, but she manages to communicate with it and send it away.
Davido tracks Octaman into a cave. The others consider abandoning the pursuit, but Davido goads them on. Octaman chases them into the back of the cave, gaining enough time to block the cave mouth and seal them in. However, Davido manages to find another way out. They return to the RV, but find Octaman waiting for them inside. In order to spare her colleagues, Lowry communicates that she accepts to be captured. Now determined to kill the beast, the remaining expedition members arm themselves and pursue the pair, only for Lowry herself to shoot the creature at close range with a concealed handgun, allowing her to escape its clutches. The expedition members fire more shots at the creature, which retreats into the lake and sinks below the surface.
