MESA OF LOST WOMEN

Feminine hands with huge, spider-like claws caress "Doc" Tucker. The hands belong to spider woman Tarantella and a brief kiss between her and Tucker ends with his lifeless body collapsing. A disembodied voice asks the audience: "Have you ever been kissed by a girl like this?"

American oil surveyor Frank and his Mexican assistant Pepe find Grant Phillips and Doreen wandering the Muerto Desert on the US–Mexico border, suffering from extreme dehydration and exposure, and take them to an oil company field hospital. As he begins to recover, Phillips feverishly asks for an oil truck expedition needed to destroy by fire "super bugs" from a secret underground laboratory on the isolated Zarpa Mesa. As he begins to tell his story from the beginning to Frank, Pepe, "Doc" Tucker and foreman Dan Mulcahey, a narrator speaks over him and shifts focus to his rescuer, Pepe, drawing attention to what the Mexicans know but the Americans would not believe.

A flashback to a year earlier shows famous scientist Leland Masterson arrive at Zarpa Mesa at the invitation of the reclusive Dr. Aranya (pronounced as araña, the Spanish word for 'spider'), whose brilliant theories have intrigued Masterson. Aranya reveals his successful experimentation with growth hormones, creating human-sized tarantulas he can control telepathically and human women with the abilities and instincts of spiders. His creation Tarantella can regenerate severed limbs and Aranya expects her to have a lifespan of several centuries. However, his experiments on male subjects have resulted in dwarfism akin to drone insects. His end goal is to create spiders with human intellect, subject to his will, to control the world. Asked to assist, Masterson instead denounces Aranya's work as evil and blasphemous. In response, Tarantella injects him with a drug that turns him into a simpleton. Following experimentation, Masterson is found wandering the desert and placed in a lunatic asylum from which he eventually escapes.

Masterson arrives in a lively bar on the border where businessman Jan van Croft and his fiancée Doreen find themselves when their private aircraft breaks down. Masterson joins the couple, and Tarantella performs a dance, mesmerizing everyone present – except for George, a nurse from the asylum who has come to collect Masterson. Masterson recognized Tarantella as evil and shoots her, then takes Jan, Doreen, and George hostage. They arrive at Jan's aircraft where pilot Grant Phillips and servant Wu are added to the hostages. Masterson forces them all to depart despite the aircraft's disrepair. Meanwhile, Tarantella regenerates following her apparent death and leaves the bar.

Grant discovers that the compass is reading incorrectly and, due to an engine failure, they crash-land on Zarpa Mesa. George is killed while exploring and Jan wounded. Grant and Doreen grow closer during the night. Jan sends Wu on a dangerous errand, allowing Wu to report to Aranya, having sabotaged the airplane in order to return Masterson; no longer needed, Wu is killed by the spider women. Blamed for Wu's death, Jan has a mental breakdown and is killed by a giant spider. The others are captured and Aranya restores Masterson's intellect, requiring his help. Grant and Doreen restrain Aranya and Tarantella, allowing Masterson to concoct an explosive in the laboratory. After Grant and Doreen escape, Masterson incinerates the laboratory, along with himself, Aranya and Aranya's monsters.

At the field hospital, Grant fails to convince anyone but Pepe of the truth of his story. It is revealed that at least one (Delores Fuller) of Aranya's spider-women has survived.