The Sheriff Jack Andrews calls the Professor Gerald Deemer. He asks him to recognize the body of a man found dead in the Death Desert, the face completely atrophied. Deemer confirms that it is Eric Jacobs, who used to work with him. A terrible quickly developed disease named acromegalia causing enlargement of bones affects him.
In his laboratory, the Professor Deemer leads secret experiences. He tests on all sort of animals a product that increases their growth in an incredible manner. There, it is possible to find rats, Guinea pigs and a tarantula of a gigantic size. But animals are not the only to have tested the product. Paul Lund, the assistant of Deemer rises suddenly, the deformed face and attempt to kill the Professor. In the struggle, the assistant will find death and the giant tarantula will escape Deemer's laboratory. This one will choose not to warn the Sheriff so as not to compromise his experiences.
But the Doctor Matt Hastings does not believe to Deemer's diagnosis concerning Jacobs's death. A crushing acromegalia never happens, it is a rare sickness that transforms a person very slowly. Hastings meets Stephanie Clayton, a student who realizes a thesis in biology and who has been engaged for the summer by Jacobs to work with him. While accompanying her to Deemer's laboratory, Matt Hastings announces her the death of her employer.
In Deemer's laboratory, Stephanie begins to work. She quickly notices what type of experience Professor Deemer is realizing. But the former has the face that changes more and more, such as if it was deforming.
By his side, the Doctor Matt Hastings inquires with the Sheriff on strange phenomenons. The cattle of a farmer have been devouring, and only bone stays. An other farmer and the two passengers of an accidented vehicle have equally been devoured by an unknown sort of animal. What is breathtaking, it is that we find identically around victims a product that is some kind of insect venom, what confirms the Arizona Institute of Agriculture to be tarantula venom.
Hastings leaves to get Stephanie and to protect her. The former is horrified by the face of the Doctor who transforms into real monster. Knowing he has nothing to lose, he explains to them that, although his product was not stable, Jacobs and Paul Lund made themselves an injection that led them to death in four days.
Hastings asks to the Sheriff to come with armed men at Deemer's while the tarantula approaches the laboratory of the Professor and attacks...
Spoiler ! the end of the story is revealed below…
Matt and Stephanie escapes just in time while the Professor Deemer is the next victim of the creature he created. The police try in any way to stop the horrible beast that does not cease to enlarge. Shootings and explosives are without effects against the immense spider that devours once more two policemen. While it arrives at the doors of the city, the aviation arrives in time to bomb the thing thanks to napalm bombing, the only arm that will finally stop it in its murderess race.
In this movie, it is nice to see the figuration of the uncredited Clint Eastwood, the Jet Squadron Leader who bombs the tarantula, at his beginnings for cinema.