Right then, apropos of nothing, here is how you do #IndianaJones5. OPEN on the Disney logo. It dissolves to a Germanic mountaintop castle. Flags flutter on the battlements. NAZI flags. The year is 1944. 
A man parachutes in, gets tangled in a tree. A fedora hat drops to the ground. The man cuts himself loose from the 'chute and scoops up his hat. This is young Indiana Jones (CGI Harrison Ford, Chris Pratt, whoever). A pistol is cocked behind him. He turns slowly, hands raised..
It's his resistance contact, a young woman who looks the absolute spit of Ingrid Bergman in Casablanca. They sneak up to the castle. Inside, the NAZI VILLAIN is about his diabolical business. His face is unrecognisable, horribly scarred, blown off in WW1.
He's plotting to turn the tide of the war with a Macguffin – the Spear of Longinus or Mjolnir or something. Indy and his partner disrupt the ritual, blow up the villain and his castle, save the day, kiss in front of the explosion, the usual. She pops his hat back on his head...
CUT TO: Old Indy, delivering a lecture to a hall full of snoozing old duffers. In the sparse crowd, one young man watches him intently. He approaches Indy after the lecture with a proposition...
He has documents that purport to show the location of the Lost Kingdom of Prester John, the mythical Christian King. It was reputed to contain wonders; the original location of the Garden of Eden, the Fountain of Youth, etc. en.wikipedia.org/wiki/Prester_J…
Cute story, says Indy, but his adventuring days are over. His curiosity's piqued, though – he can't help himself. The young man only has half the map; the other half was in the library of the NAZI VILLAIN from the prologue, the rest is in an archive in Berlin. East Berlin.
The two of them travel to Berlin, and rob the archive. They're interrupted (and helped) by a young German librarian; she's looking to escape to the West. They flee across the Berlin Wall using her route, the security forces in hot pursuit.
Success! The trio travel to the secret African location of the Lost Kingdom. There, the young man reveals his true identity – he's the NAZI VILLAIN from the prologue, healed and partially rejuvenated by a few drops of the Fountain of Youth. Nazi henchmen rock up.
His plan: secure the Fountain and use it to become the Immortal Führer ("A Thousand-Year Reich? Hitler was an amateur."). The party enters the hidden kingdom through a precarious passage, and discovers... the Garden of Eden. And dinosaurs, preserved by the waters of the Fountain.
Action sequences ensue, dinosaurs eat the Nazis, and Indy and the villain eventually meet by the Fountain of Youth. Indy symbolically rejects it. The villain beats the crap out of the old man, and steps into the Fountain. He becomes younger, and younger... a child, a baby.
Indy and the German librarian girl (who, it's heavily implied, is his daughter by the agent from the prologue) leave the Garden of Eden with the baby and seal the entrance to the Kingdom. Shia LeBeouf dies on the way back to his home planet. Roll credits.
