Mortals and picks up about nine years after the end of the first part of the story in Forbidden. There we learned that the post-war remnant of humanity is infected with a virus that removes all emotions save fear. Fear was used to keep the populace in check under the established leadership. Our hero Rom Sebastian received a vial of blood and he and several of his friends drank a portion. This blood brought them back to their full humanity by eliminating the effect of the virus. A prophesy told of a boy who would be born directly into his full humanity and that this boy would become the sovereign of the world and be the true source of the blood that would restore everyone.
This boy, Jonathan, was found at the end of Forbidden and safely hidden away until he could become sovereign at his eighteenth birthday. Rom had found a small tribe of nomads who had managed to maintain themselves away from the rest of the world. They believed in the prophesy and supported Jonathan's claim as sovereign so that they might find peace from persecution from those in power. Against this backdrop, the brother of the previous sovereign has used the dark forces of alchemy to create the biggest army assembled in the world in centuries. His goal is to crush the nomads protecting Jonathan and to destroy this boy, thus ending any possible threat to his world domination plans.
In this story, Jonathan, the man who prophesy has foretold would become the most powerful man in the world, has embraced his destiny. Yet the servant-hearted kingdom of life and restoration and atonement that he is working toward is completely different than what everyone else has assumed. He will not lead as a lion, he will lead as a lamb. A very rich story in biblical allegory that I loved. The last part of the trilogy, Sovereign is slated for release next summer.