It has been a few months since Rex's confrontations with Bathory and Vlad. Having recuperated her strength, she is now ready to focus on her next target, an alpha that hides in the shadows better than any other: Mary.

Miles from civilization, the elusive dweller lies in wait. However, the branches of this evil are far easier to find than its roots. With help from a previous acquaintance, Kaleb Isaacs, as well as his team of hunters, Rex becomes ensnared in a downward spiral of manipulated human corpses, dweller hybrids, and a beast of terrifying power.

From cloud covered streets to labyrinths of tunnels and a town forever cast in darkness, Mary seems to be a coward who attacks only from a distance. However, Rex will soon find that her white whale, Inferno, may not be in a league all his own.