During the Cold War, Soviet agents watch Professor Henry Jones when a young man brings him a coded message from an aged, demented colleague, Henry Oxley. Led by the brilliant Irina Spalko, the Soviets tail Jones and the young man, Mutt, to Peru. With Oxley's code, they find a legendary skull made of a single piece of quartz. If Jones can deliver the skull to its rightful place, all may be well; but if Irina takes it to its origin, she'll gain powers that could endanger the West. Aging professor and young buck join forces with a woman from Jones's past to face the dangers of the jungle, Russia, and the supernatural.
