In the remote mountains of California, a series of mysterious cattle mutilations and disappearances rattle a small town. Local cattlemen are puzzled and fearful of what could be preying on their livestock. Geologist Wayne Brooks, fascinated by the history of the area, theorizes that the disturbances may be linked to a legend of a Spanish Conquistador named Vargas — known as the "Diablo Giant" — who terrorized the region centuries ago, before disappearing without a trace. Brooks, along with archaeologist Dr. Frederick Cleveland and his daughter Janet, embark on an expedition to uncover the truth behind the legend and the recent disturbances.

As they delve deeper into their investigation, spurred by strange findings and the discovery of oversized, ancient armor, the team starts to believe that the legend of the Giant might be more than folklore. Their research attracts the attention of curious townspeople and a greedy treasure hunter who is convinced that the giant's burial site contains a hidden fortune. The group's scientific exploration turns perilous when evidence suggests that the giant may still be alive, casting a shadow of fear and disbelief over the quiet mountain community. As they get closer to solving the mystery, the trio must contend with mounting tensions, skepticism, and danger that threaten to consume their quest for the truth.