Tarzan is called to Brazil by an old friend, The Professor (Paulo Gracindo) to help stop the Jaguar Cult, led by Barcuma (Rafer Johnson), from destroying native villages and enslaving the survivors in his search for diamonds.

Tarzan is assisted by Captain Sam Bishop (Jan Murray), a riverboat pilot, and Bishop's young ward, Pepe (Manuel Padilla Jr.), as well as Baron (a lion) and Cheeta (a chimpanzee).

On their way they encounter Dr. Ann Philips (Diana Millay), who has witnessed the destruction of a village, and wants to continue fighting a plague by giving much-needed inoculations to natives who live along the Amazon River.

Dinky, the chimp portraying Cheeta, bit Mike Henry on the jaw during filming, requiring twenty stitches.

The chimpanzee was destroyed, and Henry later sued the producers for this accident and other unsafe working conditions on all three of his Tarzan films.