Mac Steele, a weathered archaeologist and adventurer, acquires a mysterious pre-Columbian relic that hints at the existence of a far more legendary prize: the Mask of the Sun. His investigation takes a catastrophic turn when toxic fumes from the artifact poison him, triggering a fatal biological breakdown that medical science cannot reverse. Desperate and running out of time, Steele pursues the Mask into the heart of ancient Aztec ruins scattered across Central Mexico, where he must navigate treacherous temples and decipher the forgotten knowledge of a vanished civilization in a race against his own deteriorating body.