No Rest for the Wicked by Emma Dean

A raven assassin will be her greatest ally, or her worst enemy.
Mika knew the Council of Paranormals would suspect her, which is why they assigned a raven to ‘guard’ her. But there is a ‘we’ behind the killer and she has no idea if that they are still out there, or worse, still on the island of Morgana waiting for the right opportunity to strike again.
With Malachi being distant, Ethan, Lucien, and Audrey have to work without her to follow the dangling strings, while Mika tries to win the assassin to her side. Will the raven help her unlock the secrets of her magic, or will he turn her in and be the end of everything she knows and loves?