Young Richard Lindsay (Arnold Lessing) has given up his career in science in favor of his newfound passion, surfing on the Santa Monica, California beachfront. The beachfront is located near his father and stepmother’s house, where he lives. This is to the great displeasure of his father, the noted oceanographer Dr. Otto Lindsay (Jon Hall), who is married to the younger Vicky (Sue Casey). Vicky is dissatisfied with Otto’s relative lack of devotion to her. Also living with the Lindsays is Richard’s sculptor buddy Mark (Walker Edmiston), who walks with a limp as a result of an auto accident Richard had earlier.
While Vicky hits on her stepson and teases his friend Mark, a monster emerges from the ocean and starts slaughtering the kids on the beach. Dr. Lindsay seems convinced that it is a genetically mutated carnivorous South American “fantigua fish” that has grown large enough in anthropomorphic manner to exist out of the oceans in a loathsome seaweed-shrouded form. Wiki