In the Arizona desert, Professor Gerald Deemer (Leo G. Carroll) is experimenting with growth hormones in the hopes of finding a way to increase the world's food supply. His partner in the project was recently found dead in the desert, suffering from a disease that normally takes years to advance, but, in his case, seems to have afflicted him in only a few days. The local doctor, Matt Hastings (John Agar), is puzzled by the strange case and, with Deemer's recently arrived (and very pretty) assistant, Stephanie "Steve" Clayton (Mara Corday), tries to figure out what is going on. When cattle remains are found in the countryside, evidence points to a giant tarantula as the culprit.