At the Abbey of St. Leibowitz monks have copied generations after generations the Memorabilia of Leibowitz, without understanding their meaning. Leibowitz is considered a saint but ironically the reader sees that he was a Jewish physicist and his cherished texts are grocery lists, a lottery ticket and drawings of electrical control systems. And there are hints that Leibowitz was involved in a Top Secret government project. Brother Francis, a young monk, finds a technical drawing, which is included in Leibowitz's relics and dies violently fifteen years later for a blueprint initialled by the Blessed Leibowitz. The second part, 'Fiat Lux', takes the reader to another period which has much similarities with the Renaissance.
Science is breaking free from the chains of religion, electricity is reinvented.
The dawn of a new era is embodied in the self-assured scientist Thon Taddeo. Dom Paolo, an old and gentle Abbot, doubts the blessings of the new technological inventions and tries to keep his faith in. In the last part, 'Fiat Voluntas Tua', the world is again drifting into a global crisis a nuclear war. The Order of Leibowitz has lost its power but prepares a spaceship to escape the second holocaust. A group of clergy and children leave the Earth to start their life again in Alpha Centauri.