Lord of the Abyss by Nalini Singh

Once upon a time…the Blood Sorcerer vanquished the kingdom of Elden. To save their children, the queen scattered them to safety and the king filled them with vengeance. Only a magical timepiece connects the four royal heirs…and time is running out.…

As the dark Lord who condemns souls to damnation in the Abyss, Micah is nothing but a feared monster wrapped in impenetrable black armor. He has no idea he is the last heir of Elden, its last hope. Only one woman knows—the daughter of his enemy.

Liliana is nothing like her father, the Blood Sorcerer who’d cursed Micah. She sees past Micah’s armor to the prince inside. A prince whose sinful touch she craves. But first she has to brave his dark, dangerous lair and help him remember. Because they only have till midnight to save Elden.