Ostensibly driven to mad by the Crystal Skull of Akator to the point that he'd only communicate in riddles, Harold Oxley gave Marion Ravenwood a letter in code when the pair were kidnapped in Peru by Russian soldiers under the command of Irina Spalko. 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 contacting her son, Mutt Williams, by phone and sent him the letter, urging him to get help from Professor Jones.
In the US, Mutt met Jones when he was about to leave the town and showed him the letter. After they escaped from two KGB who had been trailing them, the pair went to Jones's home in order to decypher 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. Only when he traveled with Mutt to Nazca and they found the map of the Chauchilla Cemetery on the floor of Oxley's cell at a sanatorium, he realized that the word used for "cradle" was a general word for "resting place" and that Oxley had found the conquistador's tomb, which had been lost for centuries, at Chauchilla Cemetery. There they found the burial site was guarded by warriors who wore terrifying skull masks, thus appearing as "living dead".