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 crypted message by Oxley to her son Mutt Williams. She is then recaptured.
Mutt Williams meets Jones in Bedford When he shows him Oxley's cryptic message, two KGB agents try to force them to come with them. Jones and Williams escape on a motorcycle and are chased by the KGB agents across the campus of Marshall College before they finally escape. At home, Jones deciphers Oxley's message.
Jones and Williams travel to Peru where they find the Crystal Skull in Chauchilla Cemetery. They are also captured by the Soviet Special Forces and brought to a jungle camp in Brazil where the are united with Oxley and Ravenwood.
During the Jungle Chase in Brazil, Indiana Jones, Marion Ravenwood, Mutt Williams, and Harold Oxley escape the Soviet Special Forces. They reach Akator, followed by Spalko and her men, 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.