Red Sonja: Vulture's Circle Series by Nancy A. Collins, Luke Lieberman

Following the fight to the death with one Sutekh's demonic advance scouts, Red Sonja and her prize pupils, Lyla and Xoana, return to their school with the renegade priest Sefkh in tow. After the Stygian reveals that the half-human son of the serpent-god Set is marching forth to reclaim the world for his sire, Sonja realizes that the world is in peril... moreFollowing the fight to the death with one Sutekh's demonic advance scouts, Red Sonja and her prize pupils, Lyla and Xoana, return to their school with the renegade priest Sefkh in tow. After the Stygian reveals that the half-human son of the serpent-god Set is marching forth to reclaim the world for his sire, Sonja realizes that the world is in peril. But before she can decide whether to come out of 'retirement' one last time, the school's compound is attacked by The Eaters of the Dead-a legion of flesh-eating undead created by Sutekh from those who have dared to defy him. Now Red Sonja, her longtime companion, Yusuf, and her young pupils must battle not only hell-beasts and ghouls, but the terrifying Son of Set himself in a bloody fight for not only their lives, but their souls as well. less

From shadow-haunted Stygia emerges an evil undreamt of by even the most depraved minds: the demi-god called Sutekh. Born of an unspeakable blood ritual, he is the half-human progeny of the ancient serpent-god Set, sent forth to enslave Mankind in the name