The Succubus - Castle Rehm, #1

Castle Rehm is a forgotten corner of the kingdom, where the locals spend most of their time drinking and avoiding the snow that plagues them most of the year. It's quiet, boring, and nothing at all like the bustling city where Kohar grew up. He has no problem with that, however, and in fact mostly enjoys his job as Mage-in-Residence for the most boring territory in the world. What he does have problems with are the resident Captain of the Guard, who drives him crazy on a daily basis, and Solla, whom Kohar desperately wishes would notice him but has always remained oblivious.
But then people start turning up dead, and all thoughts of aggravating soldiers and oblivious mercenaries must be set aside in the face of demonic attack and a traitor in their midst.