From publisher blurb:
Book of the Archon brings a complete collection of awe-inspiring magic to the Sertorius setting.
This is the first in a series of optional spell books that can be used on their own or combined with the spells in the original rules. Each Book of the Archon enriches play with a different take on Sertori magic. The Scrolls of Nicodemus introduces more insane power levels and unexpected flavors.
It includes a full book of spells that vary considerably in potency, new Thauma, new Objects of Power and a new monster.