Tarzan races to recover a serum stolen by a native chief. The drug is the only hope for the fever-wracked Jai, who has been bitten by a jaguar and is near death.

Tarzan is marked for murder when he clashes with a corrupt government official and his female co-conspirator. The pair are using the natives' beliefs in a monster to drive them away from a rich mineral deposit.

Tarzan becomes concerned when news reaches him of plans to build a dam in a geologically unsound area. He needs to prove the weakness in the plan and why none of the government surveys in the area have not uncovered the same issues.