Chud.com isn't known as a site that posts wild, unsubstantiated rumors, so I'm taking fairly seriously their claim to have unearthed the plot backbone of 'Indy 4' -- consider this your official spoiler warning. A so-called reliable source has told the site that the storyline of the film will take its cues from two areas: first, a 1968 book called Chariots of the Gods, which hypothesized that the technology and religion of ancient civilizations were a by-product of their being visited by an alien race. Examples range from Biblical passages that describe spacecrafts to the famous Nazca lines in Peru -- ground-level drawings of such a scope they can only be seen coherently from the air, begging the question as to how they were done by a primitive culture. The film's plot will also involve 'crystal skulls' -- a phenomenon with some basis in fact. Over the years, explorers have unearthed a handful of models of human skulls fashioned out of clear quartz crystal. The most famous one was supposedly found in a temple in Honduras, and the skulls are said to have any number of mystical properties and origins -- Aztec, Atlantian, you name it.
The source also tells Chud that Shia LaBeouf's character will be a 'greaser' -- think Marlon Brando in The Wild One, with greased back hair and leather jacket and denim jeans. At some point in the story, he will come into contact with Indy, but the two will not discover they are related until a "pivotal action scene." The source also says that the opening action scene of the film will pit Indy against Soviets in Area 51. The fact that Chud closes by noting that the script is still being worked on also strikes me as legit, since Sean Connery seems to have said the same thing in an interview only a few days ago. Who knows how all of this will fall into place.