Narrated by actor Memo Sauceda, MYSTERY OF THE MOUNTAIN: HIDDEN IN PLAIN VIEW chronicles a most intriguing and remarkable story, and explores the question: what if one of the world's largest pyramids is waiting to be unearthed in Mexico? For centuries, a rugged and venerated hilltop in Mexico has borne witness to the rise and fall of pre-Columbian societies, and to the creation and destruction of temples and pyramids. It is also the focal point of a most unlikely mystery, and a possible sacred structure lost to history. The program investigates one of the few clues that remains today: a 430-year-old map that was carefully redrawn and passed down from generation to generation. The map depicts what would be one of the largest step pyramid structures in known history.