The Book of the Created - The One Book, #3

AND SO THEY DEPARTED, BOUND FOR THE REALMS OF HELL, WHILE BEHIND THEM ROME BURNT. In The Book of the Created, the third volume of The One Book series, David continues his journey to the lowest Spheres of Man to heal the world. Accompanying him are three companions: Sister Angelina, an Advocatus Dei for his canonization; the created man, an artificial being who serves as a catharist; and the lieutenant, an unbeliever and David's reluctant protector.
Descent has become precarious, and many of the still-functioning Assumptions that link the Spheres, once under the stewardship of the Jesuits, are derelict or have been seized by warring factions who impose their ideologies on any wishing to pass. Amidst this tumult, and torn between his love for his companions and his vow to the Angels, David is forced to confront the unquestioned assumptions he holds about his world - and to make a series of gut-wrenching decisions that affect not only their fate, but the fate of every living soul in the Spheres of the Apostles.