As with Raiders and Temple, once the third act of Kingdom comes, the concerns of the movie turn largely physical -- how do we get the thing from the bad guys, how do we get to the sacred temple before them, how do we get a car-boat into a river, etc.
But first, Indy has a piece of important personal information revealed to him.
Mutt, acting very Indy-like, facilitates an escape from Spalko's camp, leading Indy, Marion and Oxley into the jungle. They don't get far before Indy and Marion stumble into some quicksand. Mutt goes off to find something to extract them and Indy sends Oxley for "help." Neither of these motions makes any sense -- it's a jungle, and there are vines shown covering every tree and rock in sight, why should Mutt need to go off to find anything, and Indy expects Oxley to go off and get help from who, exactly?
The answer is, of course, that the screenplay needs to have Indy and Marion alone for a moment so that Marion can tell Indy that Mutt is his son. The path to the scene may be hastily constructed, but the resulting moment is sweet, comic and thematically important. Indy, headstrong master of improvised action, suddenly finds himself stuck in encroaching old age, with an old girlfriend, no less, and now, out of nowhere, a new son, new responsibilities and a whole new set of priorities. What better way to express the protagonist's new situation than putting him in a pit of quicksand? And what do he and Marion discuss? Mutt's education, of course, tying the scene to the theme of knowledge and experience. This is the scene the whole movie pivots on: in the second half of Kingdom, Indy finds himself shifting in his role from lone adventurer to responsible patriarch.
Spielberg has explored this notion before, that in a world where nothing makes sense any more, people turn to the family unit for answers about how to live one's life. It is the opposite of the young Spielberg, where his protagonists could not wait to get out of the family unit in order to pursue their various obsessions.
In any case, Mutt returns to help his mother and father out of the quicksand -- an example, perhaps, of the child bringing the parents together, and Oxley returns with Spalko and her goons, creating a situation rare in Spielberg, where the characters, after a set piece, find themselves in the same position they were in before. What makes this dramaturgical no-no permissible is that Indy is, literally, not the same person he was when he entered the quicksand. Now a father with a wife and a child and a friend, he can no longer afford to tell the bad guys to piss off -- he has to play ball or else his family will be destroyed. What father could not identify with this situation? Mostly a father these days just needs to worry about pleasing an unqualified boss, not capitulating to the demands of a wild-eyed Soviet dominatrix.
What is Indy thinking at this point? Well, speaking as a Hollywood screenwriter, I would say that Indy's thinking: a) I must protect my family, b) I must help my friend recover his sanity, c) maybe the way to do those things is by doing the thing I'm good at, and d) maybe that means that I can pull it all together -- gain knowledge and protect my family and friend at the same time.
Which catapults the narrative into the "drive through the jungle" sequence. Indy and Mutt stage a family fight (about, what else, the acquisition of knowledge) in the back of a truck carrying them to their final destination. (The rather fantastical jungle-cutting vehicle at the front of the procession prompted Sam to exclaim "Hey! Just like Speed Racer!") Indy, working with Mutt and, eventually, Marion (who does not seem to have been in on the plan, but is certainly up for improvising) turns the dynamic of the drive through the jungle, hijacking both the antagonist's agenda and the artifact driving the pursuit -- the crystal skull. So, while Indy and Mutt pretend to debate education, they are, in fact, creating education's antithesis, experience. No college course could instruct Mutt how to swordfight with a psychic Russian in a Lulu bob during a high-speed pursuit through the Amazonian jungle.
During the sequence, of course, Mac reveals himself to be a "good guy" after all, another reminder that, if you need to have an expository speech, the middle of a dynamic chase scene is a good place to put it.
(And let's remember that Mac, like Oxley, are not really "characters" at all -- they are reflections of the protagonist. Oxley is the pure academic, who has gone crazy from his pursuit of knowledge, Mac is the wayfaring capitalist whose virtue can be bought for a sack of gold. Mutt, in addition to being Indy's son, is also Indy's reckless, driving intuition. People have been complaining that Indy doesn't have enough to "do" during the last half of Kingdom, but overlook the fact that Indy is, dramatically, the bulk of the cast at this point.)
(The drive through the jungle pauses for a fight among some Army Ants. I would like to say that this sequence is a reference to Antz, but that is probably in my imagination. Although let me also add that, in the one Antz story meeting Spielberg attended, he interrupted a conversation between myself, Nina Jacobson and Jeffrey Katzenberg to pitch a "battle with the army ants" scene -- so apparently army ants have been on his mind for quite a while. Army ants, of course, owe their success as a species to their possession of a hive-mind, which becomes important later in Kingdom.)
(Mutt gets cut off from the main chase and employs a Tarzan move to rejoin the group, a reference that even my 5-year-old daughter got, although she probably did not also stop to consider Tarzan's innocence/experience dichotomy. Mutt, lacking in education, is taught by a bunch of monkeys to swing on vines. The story of Tarzan, of course, hinges on the protagonist's conflicting feelings on the "purity" of his animal innocence vs. the pull of civilization, "where he belongs." Mutt feels a similar conflict, and the Tarzan moment, cheesy as it may seem to some, is thematically resonant.)
Once the maguffin is in Oxley's hands, Marion drives their car-boat off a cliff and into a tree, a situation the protagonist of Jurassic Park would be familiar with, only this time, of course, Spielberg stands the stunt on its head, making it intentional and beneficial. The plunge into the river leads to some waterfalls and the final drive into Act IV.
Indy takes the skull from Oxley, prepared to take it to wherever it needs to go by himself. Why? "Because it told me to" : this is, apparently, what the skull imparted to Indy during their little tete-a-tete. This adds yet another wrinkle to Indy's priorities: he must protect his family and friends, he must pursue his desire for knowledge, and now he must do what the higher power instructs. This last makes the elderly Indy a cousin to Close Encounters' Roy Neary, the implications of which will become clear shortly.
Indy and his family make it through the waterfall and to the temple-thing, pursued by Spalko and her surviving goons. Indy and his family are chased by Indians, whom they subdue with the power of the skull. Indy subdues the natives through religion, while Spalko subdues them the old-fashioned way -- with sub-machine-gun fire.
(The subduing of the natives plot-point led to this after-movie exchange: KRIOTA WILLBERG: "So wait, the skull works on army ants -- and natives?" JACKSON PUBLICK: "Well, but come on -- the skull is central to the natives' entire belief system!" Mr. Publick may have been disappointed with Kingdom, but he wasn't going to stand by and let some choreographer needlessly nitpick over issues of logic -- that would lead to questions about, like, how a carload of people survive plunges over three waterfalls, and don't drop their skull-bag.)
We get to the "throne room," where it becomes clear what needs to happen -- the skull must be put back on the head of one of 13 alien skeletons arrayed in a circle of thrones. Indy, for the first time in his career, is hesitant to take this final step, and this is, in a way, his cumulative moment. Presented with the goal, he backs off, reluctant to take his journey to its logical conclusion. The reason being, he has experienced enough of the skull's power and knows that pursuit of ultimate knowledge can only lead to insanity (that is, Oxley) and maybe something much worse.
And maybe it's just a coincidence, but maybe the bulk of Kingdom takes place in a jungle in reference to the original jungle, the Garden of Eden. The reference is never explicit (ie, nobody reaches out and takes a big healthy bite from a juicy red apple), but the crystal skull is, essentially, the apple from the Tree of Knowledge. Gazing into the skull (that is, biting into the apple) will give you knowledge, but you will also become a different person because of it. The younger Indy may have taken the risk (as Oxley did) but the older Indy has too much to lose. On the other hand, Indy was wise enough in Raiders to close his eyes to the fury of the Ark -- whether out of a sense of responsibility to Marion or for his own self-preservation.
Anyway, Mac is revealed to be a straight-up amoral capitalist, the "grave robber" Indy denied being in Act II. He brings Spalko to the throne room and takes the opportunity to go loot whatever he can out of the rest of the temple.
Spalko takes the skull from the reluctant Indy and replaces it on the alien-skeletons's neck, setting a big whirling thing in motion. The temple, we find, is a huge, buried spacecraft -- science interpreted by humans as God -- and, like the aliens in Close Encounters, their only desire is to "go home," which they apparently cannot do until their missing skull is returned.
An inter-dimensional portal opens in the ceiling, carrying debris and Soviets to who-knows-where. Roy Neary would have jumped at the chance to pursue this ultimate knowledge, that is, to know God, but the older, wiser, Indy knows that one does not, cannot come back from that particular undiscovered country. Seeing the portal open, Indy grabs his family and runs as fast as he can in the opposite direction. This direct, conscious repudiation of the thesis of Close Encounters is the most striking of Kingdom's conceits and the thing that puts it into a higher realm of "importance" in the Spielberg canon.
(I've seen several people complain that Kingdom steals its central plot-points from Stargate, but I put the theft much earlier: Eric Von Daniken's Chariots of the Gods?.)
Spalko, of course, receives what she has come for, which is, essentially, what Dave Bowman gets at the end of 2001: all the knowledge in the universe. Dave survives the process of education, and returns to Earth to do who-know-what. Spalko does not survive, although perhaps she gains some measure of godhood in whatever plane of existence the acquisition of all knowledge she achieves.
Indy, on the other hand, would rather be a simple husband and father in this world than a maybe-god in another. Having been uprooted from his own life, he has re-discovered his identity. By replacing the thing that was stolen, he regains what was stolen from himself.
But that doesn't mean he's going to let Mutt wear his hat.