A large octopus terrorizes a seacoast town in California. The story begins with it attacking a fishing boat in a bad storm. Sailors shoot at it, with no effect on the beast. The boat capsizes from a huge wave because no one is in the bridge. A tentacle smashed a window in the bridge and the crew was afraid to man the steering wheel. They manage to send an S.O.S., picked up by a Coast Guard Cutter and Doctor Jeff Thorpe, a Marine Biologist. The cutter goes to the area of the stricken vessel, but they find nothing. The boat has already sunk. Doc Thorpe consoles the captain