Meanwhile, on Nazi Island, Indy and Marion are, to Indy?s surprise, the guests of honor. They meet the head of the community, a beautiful woman named Blanca Frensiska. She tells them that they hold Indiana Jones in high esteem, for having been a worthy enemy during the war. She agrees to give them a ship to travel to Antarctica, but asks that she come with them. Thus, Blanca, Indy, Marion, and Jock set sail through chilling waters, and Blanca is revealed to have developed a crush on Indy, which infuriates Marion. Jock, meanwhile, serves as comic relief. They eventually reach the archway, and travel through it, arriving in a dense jungle. The foursome travel down a river, and soon reach a large city inhabited by all young people.
Meanwhile, Mutt and Irina are flying towards the Arctic, and fly through the archway. They enter the world, and arrive at the city, where Indy and Marion are amazed to see Mutt, and are highly suspicious of Irina. The group is brought to the temple, where the garden containing the flowers is kept. The people try to convince Indy and the others to take the elixir, as they are obsessed with eternal youth, but Indy is nervous about doing so. That night, Irina meets Mutt in his chambers, and she tells him to come with her. They both sneak into the temple, and pluck some flowers.
Irina tells Mutt that they can escape in the plane, and live together in hiding, taking the elixir when they have gotten old. Mutt decides to go along with it, and thus him and Irina sneak into the plane and fly off. But they don?t notice that Indy has stowed away on board, and Indy confronts Irina, correctly accusing her of still working for her father, having lied about wanting to stop him, and she was going to bring the flower to him after killing Mutt. Irina admits it, and she fights with Indy using martial arts, as Mutt tries to fly the plane, in a humorous mirror of the previous plane fight.
Mutt manages to land the plane, and Indy knocks out Irina. They fly back to the city, and the young people lock up Irina. Mutt is heartbroken by Irina?s deception, and Indy comforts his son by telling him about his own experience with Elsa Shneider. Just then, the Youthfuls, as we?ll call them, decide to have Irina sacrificed to their god. But during the ceremony, Indy convinces the Youthfuls to spare her, and they agree. Indy meets with Irina, and she tells him that she owes him her life. They have an emotional moment, in which Indy reveals what really happened to her mother.
That night, Blanca enters the temple, now with guards stationed, and she kills them. She steals some flowers, and rushes out of the temple towards the plane. However, Marion, who was up early that morning, sees her, and they get into a brutal fistfight. Indy and Mutt arrive, and Indy is forced to shoot Blanca to save Marion?s life. As Blanca lies dying, she reveals that her plan was to steal the flowers so that she could make the elixir to keep her people immortal. She then passes away, with Marion spitting on her body. The next morning, our heroes decide to return to their world, deciding to leave the Youthfuls alone, as immortality should be kept secret from the rest of mankind. Indy, Marion, Mutt, Jock and a tied-up Irina board the ship, and drive out of the archway.
But the moment they go through, they see a Russian warship waiting for them. They are captured, and Makovsky reveals himself to Indy, brutally torturing him. Irina is untied, but she finds herself now doubting her allegiance to her father, and is bound by her sense of honor to help Indy and his friends. Thus, she decides to aid them in escaping. She takes grenades, and blows up the ship?s engines. In the distraction, she helps our heroes break free, and as they are boarding their ship, Makovsky engages Indy in combat. They fight, and in the battle Indy loses an eye. He manages to defeat Makovsky by kicking him into the water, where sharks devour him.
Irina is about to get onto the ship too, when a Russian soldier shoots her in the gut. As Indy steers the ship away from the sinking Russian vessel, Mutt holds the dying Irina, and forgives her as she passes away. Indy and Marion comfort Mutt, who is devastated. A few months later, Indy is back at Marshall College, and he is teaching his class when Mutt walks in the door, and sits down, thus revealing that he is now a student at Marshall. Indy smiles, and continues his lecture.
THE END