Heaven's Messengers begins with the death of six young people—three in Mexico, two in the United States, and one in Spain.

All are admitted to heaven by St. Peter and given special assignments to interview six important personages in the conquest of Mexico: Hernando Cortés, Pedro de Alvarado, and Martín López (the last far less well known, but he was a master carpenter and boat builder who constructed thirteen small vessels that were launched on Lake Texcoco and provided a naval component that proved vitally important to the success of the conquest); Doña Marina and Isabel Moctezuma, both Aztec women); and Leonor Cortés Moctezuma. The six messengers are miraculously returned to life and placed in the century of conquest with specific assignments—to illustrate how three men steeped in Roman Catholicism and three pagan women become worthy.