The Undead Pool (Hollows Series #12)

Witch and day-walking demon Rachel Morgan has managed to save the demonic ever-after from shrinking, but at a high cost. Now, strange magic is attacking Cincinnati and the Hollows, causing spells to backfire or go horribly wrong, and the truce between the Inderlander and human races is shattering. Rachel must stop this dark necromancy before an all-out supernatural war breaks out.

Rachel knows of only one weapon to ensure the peace: ancient elven wild magic, which carries its own perils. And...