The Demon King.

In this final entry of 'The Nightfall Saga', Olive and Darin pursue the Demon King to a strange new land across the sea. There they discover a culture unlike any they have never known, where demons live alongside humans as servants and companions. And there they meet the demon's masters - including a seductive prince who is drawn to Olive - who seem unable or unwilling to understand the danger they are in. Because no human is safe from the Demon...