Marion Ravenwood receives a letter from Oxley which makes her believe that he is mentally disturbed, and she travels to Peru to look after him. She gets caught by the Soviet Special Forces as well, but they let her escape long enough so that she can send a letter together with a new letter by Oxley writtten in cryptic symbols to her son Mutt Williams. She is then recaptured.
Mutt Williams shows Oxley's letter to Jones who deciphers the cryptic message. The two travel to Peru and find the Crystal Skull in Chauchilla Cemetery where they are also captured by the Soviet Special Forces.
During the Jungle Chase in Brazil, Indiana Jones, Marion Ravenwood, Mutt Williams, and Harold Oxley escape the Soviet Special Forces. They reach Akator and return the crystal skull.
Akator is destroyed and the valley flooded with the waters of a nearby river when interdimensional beings take off with their ship.