Here is a short rundown of the plot formula used by George in the three Indiana Jones movies. We posted this a few months ago and dug it out of our archive pages with a few minor modifications added.

RLA = Raiders of the Lost Ark
TD = Indiana Jones and the Temple of Doom
LC = Indiana Jones and the Last Crusade

1) Movie opens, Indy Jones is searching for artifact, gets artifact, loses it to the "bad guys"

RLA--> South American Idol
TD---> Lao She's Ashes
LC---> Cross of Coronado (although he got it back on the ship)

2) Takes a plane with/meets woman

RLA--> Marion in Nepal
TD---> Willie in Shanghai
LC---> Elsa in Venice

3) After/during plane trip, they are sabotaged/attacked, get info on mission/clue , sidetrack to new destination with large old building(s)

RLA--> in Nepal attacked by Nazi henchman, get headpiece, go to Cairo to scope out buried city Tanis for the Ark
TD---> pilots leave them with a fuelless plane in the mountains, land in Village get info about stolen children and Shankara stones, go to Pankot Palace to check out story
LC---> attacked by members of the Cruciform Sword, get info about Grail on shield and info about Henry's whereabouts, go to Castle Brunwald in Austria

4) Female heroine is captured at some point

RLA--> Marion captured in Cairo market square
TD---> Willie caught while watching Indy scope out the Stones
LC---> In Castle Brunwald, Elsa taken hostage by Nazi stooge

5) Must have one showcase phobia-inducing animal.

RLA--> Snakes in Ark pit in Egypt
TD---> Cockroaches/insects in cave tunnel
LC---> Rats in knight's tomb in Venice, Italy

6) Showcase action scene with special vehicle with Indy w/jacket+hat

RLA--> Truck containing the Ark scene where he goes under the truck
TD---> Minecar scene where they escape Thuggees and water
LC---> Tank scene where they fall over the cliff

7) After goal (artifact) is found, it kills the bad guy(s)

RLA--> Nazis and Bellock die after opening the Ark
TD---> on the bridge hanging over the cliff, Indy recites some words, Mola Ram dies trying to catch one of the flaming Shankara stones
LC---> Donovan dies after drinking from the wrong Grail

8) Ending scene(s) must contain a cave

RLA--> the island cave where the open the Ark
TD---> Thuggee temple under the palace
LC---> the Grail cave

9) Indy loses/gives main artifact to someone else

RLA--> U.S. Government takes the Ark from Indy and hides it in some wharehouse
TD---> Indy gives the enchanted Shankara stones to the village people
LC---> The Grail falls into a crevice in the earth's crust and is presumed to be hidden forever

Will the script to Indiana Jones 4 follow this template? Who knows . . . but it would be a safe bet that George, Steven Spielberg and Harrison Ford will stick with what has worked in the past.