Diamond Crown of Yucat¿n follows two parallel stories that blend mystery and history: a contemporary story about an archeological expedition in Mexico, and another story about Medieval Yucat¿n that goes back to 1519. In the present-day story, Professor Cronin, a great expert in ancient Maya civilization, shares a ÒhereticalÓ idea with his colleague Katrin: long before the Spanish invasion of Mexico in the 16th century, the majority of Maya Indians lived under Christian laws. A thousand years ago, Christianity was brought to them by their ancestors Ð the Tatars-Toltec. The Professor plans an archeological expedition to Cozumel to search for evidence to support his theory. He invites Katrin and her ex-boyfriend to join the expedition. Katrin is looking to have fun in Mexico and participate in the search for an ancient artifact Ð the Imperial Crown of Yucat¿n, but she begins to suspect her ex-boyfriend in a double game. The day before the departure, she discovers the murder of a member of the expedition.