Through a Crimson Veil - Crimson City, #1

When a sexy half demon asks Conor McCabe for protection, he can't say no and he doesn't understand why. He hates demons. He doesn't want to help her. He doesn't want to want her, but every minute he spends with her strengthens his need to keep her safe-and intensifies the desire burning between them. Mika Noguchi sought out Conor to steal the key that can free all demons imprisoned in Orcus. She quickly regrets her mission-Conor is her destined mate and he'll view her theft as betrayal-but she gave her word to the council and the penalty for breaking it is severe.
Other demons are loose in Crimson City, however, and they have their own plans. They're not about to let anyone stand in the way. Not Conor. Not Mika. They'll do anything it takes to advance their agendas-even kill. This is the third book in the Crimson City series.