Knight's Retribution (Knights of Hell #6)

Rocco thought he knew pain and sacrifice...until demons dragged his female to the depths of Hell. Knowing he failed to protect her—and that her fate is in the hands of pure evil—is driving him to madness. With time running out, he'll do anything to bring her home; even embrace the unrelenting inner darkness he's fought his entire life.
Each day Kyler prays for death but there is no mercy in Hell. Lucifer's twisted son Diemos controls her every waking hour, waiting for her dormant powers to finally unleash so he can use them himself. Sweet dreams of Rocco are her only escape—but only in her wildest fantasies did she imagine him walking through the fires of Hell to save her.
Now Diemos will stop at nothing to get Kyler back. A brutal battle is coming, and to survive, everyone will have to fight. Win or die—there is no second chance for the Knights and their mates.