After Marion Ravenwood had received Oxley's first letter, she believed he was mentally ill and followed him to Peru to care for him. There, she was abducted by Soviet Special Forces under Colonel Irina Spalko who also had abducted Harold Oxley before.
Apparently driven to mad by the Crystal Skull of Akator to the point that he'd only communicate in riddles, Oxley gave Ravenwood a letter in a cryptic code that he had written before he was captured. With the Soviets searching for Akator, they allowed Ravenwood to escape long enough so that she would get the letter to Indiana Jones to translate. Ravenwood unwittingly followed through on the plan by sending a letter to her son, Mutt Williams, urging him to get help from Professor Jones and enclosing Oxley's cryptic message. She also contacted Mutt by phone, indicating that she had sent him the letter, but during the phone call she was recaptured by the Soviets and the line went dead.
In the US, when Mutt received Marion's letter, he rode on his motorcycle to Bedford where he met Jones at the train station when he was about to leave the town. He took him to Arnie's Diner and showed him the letter. After they escaped from two KGB agents who had been trailing them, the pair went to Jones's home in order to decipher the message.
The letter contained figures and text which Jones identified as being Koihoma, an extinct Latin American language with Pre-Columbian syllabic base. The text contained a riddle, which he translated as:
- "Follow the lines in the earth only gods can read which lead to Orellana's cradle guarded by the living dead."
Jones correctly interpreted the "lines only gods can read" as the Nazca Lines in Peru which can only be seen from above. However, he did not understand the reference to Orellana's cradle because Francisco de Orellana had been born in Spain.
Jones and Mutt took a flight to Peru and found a map of the Chauchilla Cemetery on the floor of Oxley's cell at Nazca sanatorium. Jones then realized that the word used for "cradle" was a general word for "resting place" and that Oxley had found Orellana's grave which had been lost for centuries. Arriving at the cemetery, they found the burial site was guarded by warriors who wore terrifying skull masks, thus appearing as "living dead".