The Mayan Secrets" is the fifth book in the Fargo Adventure series by Clive Cussler and Thomas Perry. Here's a summary: Sam and Remi Fargo, a wealthy couple with a passion for treasure hunting and archaeology, are in Guatemala providing aid after a devastating earthquake. While hiking to a remote village, they stumble upon an undiscovered Mayan archaeological site and discover a codex that could revolutionize our understanding of the Mayan civilization. The book contains astonishing information about the Mayans, their cities, and even mankind itself. However, the secrets within are so powerful that dangerous individuals, including hitmen, drug runners, and a wealthy villain, will stop at nothing to possess them. As the Fargos race to protect the codex and uncover its mysteries, they traverse the jungle, discover hidden Mayan sites, and narrowly escape death.