It's 1981. Marion's long since dead and buried, Mutt's moved out west and settled down. Indy's retired. He's in surprisingly good shape for his age, but... he's all alone. He's outlived his time. Now he's learned he's terminally ill with cancer - two months, maybe six weeks left to live. In the meantime he can do what he wants. In a few more weeks, he won't feel like doing much. One thing Dr. Jones is certain of - however he goes out, he'll be damned if it's wasting away in a bed in agony.
As if on cue, he gets a call from those 'top men' (CIA agents this time) again. There's a three-way race going on. The Americans, Soviets and Chinese have gotten a lead on a mystical item: The ring of Genghis Khan, supposedly originally worn by King Solomon and given to that ruler by God Himself. With that ring, Genghis and his Mongols nearly overran the medieval world. And it's said whoever finds it will become the ruler of the world.
Of course, the top men don't believe in the story of its magic. But they don't want to find out what that ring on the finger of Xiaoping, Brezhnev, or even Reagan might lead those men to. Indy's asked to accompany/advise the American expedition (unaware of the CIA's actions), find the ring first, and - at all costs - destroy it.
Oh - did I mention this gold ring, in addition to a ruby, has a swastika on it? (A later addition by Genghis, not original.) Which brings Neo-Nazis in and makes it a four-way chase. And soon, the American expedition is all but wiped out and Indy's the only other one left...