Tempest by Karen Lynch

Danielle Danshov has wanted to be a warrior for as long as she can remember. At eighteen, that dream is within her grasp – if she can get through her final year of training, master her Fae magic, and work with the enigmatic new trainer who challenges her as no one else has.
Outside Westhorne, a sinister new threat is growing, and demons and shifters are disappearing without a trace. As the Mohiri search for answers, danger strikes close to home, and the investigation becomes a race to save someone Dani loves before it’s too late.
When Dani’s world begins to crumble around her, she must find strength she never knew she had and harness the power inside her. She’ll need both when she faces her enemy and discovers just how much she has to lose.

NOTE TO NEW READERS: Tempest takes place in the Relentless world twenty years after the events in that series. There are numerous references to people, places, events, and creatures from the original series. If you are new to Relentless, it’s recommend you read that series (or the first three books) before you read Tempest.