When the demonic Horde threatens to unleash Hell on Earth, two women must summon every bit of their shared power to save the world.

Grace Carter, a “source” of magic, has spent the last nine months searching for Maggie Mulvaney, her “catalyst.” The joy of reuniting with her partner—and her lover—is thwarted by her worst fear: Maggie doesn’t remember Grace or their life together. Grace blames the Order of Saint Teresa, the centuries-old organization that trained them to be the strongest demon-hunting duo in generations. But why has the Order done this?

As Maggie and Grace begin to piece their lives back together, they discover that their memories have been masked by someone within the Order. Should the Horde succeed in their plan, those who have committed their lives to slaying worldly demons will be relegated to little more than minions as humans are completely enslaved.

Now, Grace and Maggie must sacrifice everything, possibly even their lives, as they battle to save humanity.