As the film opens, a small boat is seen chugging through stormy seas. A gigantic octopus appears from the ocean and seems bent on killing the sole crew member on deck. Suddenly, the octopus releases the man and retracts its tentacles from the boat. Relieved, the sailor peers out the porthole, only to see Gaira, a large green humanoid creature, fighting the octopus. After easily defeating it, Gaira turns his attention to the boat and sinks it.