Peter Collins and Rosa Guzman, having passed their first round of tests in ancient Mexico, are again summoned by the Plumed Serpent who flies them back in time to the first morning of the world. There, the sixth graders witness the origins of human sacrifice as gods throw themselves into the sluggish sun that refuses to rise despite receiving divine fuel.
Finally, Quetzalcoatl, the Serpent, blows a hurricane-force wind that lifts the sun and whisks the children to Tollan Two in tenth century Mexico. They meet the young king, Topiltzin, who has banned human sacrifice in Tollan. But his neighbors, the Chiminec, worship Smoking Mirror who demands mass human sacrifice as the price for military victories. The Chiminec declare war on Tollan.
Topiltzin proposes an alternative to war. He challenges his neighbor to the sacred ball game which re-enacts the drama of the rising of the Fifth Sun. The winner is to be given complete power over the loser. All members of the losing team will be put to death. Tollan's team includes Topiltzin, three of his finest warriors, and Peter, who volunteers despite Rosa's protests.
The outcome of the game produces profound changes in Mexico as well as in the lives of Peter and Rosa.