The Hearth Witch's Guide to Magic & Murder by Kiri Callaghan

"When a rise in London's supernatural crime puts Fey society at risk of discovery, the Winter Council turns to an unlikely solution--Avery Hemlock, the changeling they sentenced to 500 years of nightmares. Inherently lacking social grace and missing approximately two centuries of world knowledge, Avery must find a way to acclimate and solve the case or lose her probationary freedom"--