THE BEACH GIRLS AND THE MONSTER

Three surfers and their girlfriends are at the beach when one of the girls, Bunny, runs away from her boyfriend in fun. She is found dead near a cave after being attacked by a seaweed-covered lizard humanoid creature. The sheriff finds mysterious footprints left in the sand, and takes a cast to the laboratory of Dr. Otto Lindsay, a leading oceanographer. Dr. Lindsay's opinion is that it could be from a "fantigua fish", a carnivorous maneater, which has grown large enough to exist out of the ocean in a loathsome seaweed-shrouded anthropomorphic form. The Santa Monica, California beachfront is near Dr. Lindsay's house, and he complains about the "loafers" and "little tramps" who hang about there.

One of these is his son, Richard Lindsay, who used to assist Dr. Lindsay with his studies on mutation. The other members of the household are Richard's salacious stepmother, Vicky, who feels neglected by her older husband and drinks and flirts; and Richard's friend Mark, a sculptor, who lives in the connected guest house, and walks with a limp after being injured in a car accident caused by Richard. Since the accident, Richard wants to live more for the moment and for his girlfriend Jane, and is unwilling to return as his father's research assistant, to his great displeasure. Mark advises Richard to get along with his stepmother and father. They view a film of surfing in Hawaii.

The next day, Richard and Jane avoid the beach and swim in the pool. Vicky goes to the beach alone, and unknowingly almost becomes the creature's next victim. She returns home and models for Mark, taunting the frustrated sculptor who is attracted to her.

Dr. Lindsay again tries to persuade his son to rejoin his research, but Richard prefers to go to a night time beach party, despite the killer on the loose. Dr. Lindsay returns home, where his bored and dissatisfied wife informs him she is leaving him to make a new start. He overhears her then making a date with another man.

During the dancing and music at the beach party, the creature attacks a surfer, Tom, who is left dead and slashed across the face. Mark sees the attack but is unable to prevent it; he finds a strange strip of rubber in the sand.

A very drunk Vicky returns home, and finds a typed note purportedly from Mark asking to speak to her in his room. There, she is attacked and killed by the creature, and her face hideously scarred. Mark returns, and finds a rubber mask in the kitchen cupboard. The creature attacks him. After a struggle, he stabs the creature with a kitchen knife and tears off its mask to reveal Dr. Otto Lindsay, who escapes in Jane's car. Richard and Jane return to find Mark dying. They inform the police and go with the sheriff, joining the car chase in pursuit of his father. The wounded Dr. Lindsay loses control of the car and is killed in a fiery crash. The sheriff theorizes that Dr. Lindsay was doing it for Richard.

The creature is revealed to be Dr. Otto Lindsay in disguise. After a struggle, he is mortally wounded and dies in a fiery car crash while fleeing.

The ending unmasks the true monster as Dr. Lindsay, blending the horror of the unknown with a tragic family twist. His demise brings closure to the killings, but suggests deeper motives tied to family and resentment, giving the film a melodramatic edge that rises above its creature-feature trappings.