A cave mutant, wearing a necklace with raw gemstones, rekindles interest in a fabled underground kingdom where jewels cover the ground. Denea, the daughter of a renowned archaeologist, hires a pair of salvage investigators to help. A professor and his protege join the expedition to explore the caverns near the site where the mutant's necklace was found. They soon encounter a whole band of mutants who capture Denea and try to roast her on a barbecue spit. Next, they encounter a cave-girl fleeing the mutants. While following her, they meet a robot who shoots fiery green balls of light. Breaking out into an open area, they an alien queen who is hoping to repair the damaged spacecraft in which she crash-landed. The area is also inhabited by various dinosaurs, some of which engage in mortal combat. Eventually, the crew finds a few gemstones, fill their pockets and packs with them, and run for the exit in a borrowed land cruiser. The tunnel proves too tight for it, so they bail out just in time for the vehicle to explode.—Garon Smith