Marion Ravenwood receives an iritating letter from Harold Oxley and travels to Peru to look after him. She gets caught by the Soviet Special Forces, too. Later, the soviets appearently let her escape so that she can sent a letter together with a cryptic note by Oxley to her son Mutt Williams, after which she is again captured by the soviets.
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 distroyed and the valley flooded with the waters of a near-by river when the Interdimensional beings take off with their ship.