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.

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.

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.

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.

[3] All Mark's "sculptures", the creature's head, and the "Kingsley the Lion" puppet used in the film, were created by the actor who played Mark, Walker Edmiston, the host of The Walker Edmiston Show, a children's television program in Los Angeles, which featured original puppet characters, including Kingsley the Lion.

[4][1] The score for The Beach Girls and the Monster was arranged and conducted by Chuck Sagle, and a few of the musicians assembled for the soundtrack were members of the surf band The Hustlers (who are known for their songs "Kopout," "Inertia" and "Wailin' Out") from Riverside, California.

[1] Writing in AllMovie, reviewer Cavett Binion described the film as a "hysterically awful rubber-suit monster romp" with "a certain ugly charm, according it "so-bad-it's-good" status.

[citation needed] In 2019 film was used as source material in surf rock band Robert Shredford's music video for the song "Shreddy Betty".