Women of the Night; Book 1

Seraphina Alastair and Celeste Whitlock were childhood friends, with the makings of being lifelong besties. However, after Celeste's father dies in a mysterious house fire, she and her mother disappear, leaving Seraphina to wonder what happened to her best friend.
Twenty years later, Celeste is shocked to be called "Dean" - a nickname she hasn't heard since the death of her father - when she rescues a familiar woman from a malicious ghost. The two friends reunite and Dean explains that she's on the hunt for her missing mother.
Bored with her mundane life and unwilling to let her friend go again, Seraphina leaves everything behind to help Dean's hunt, even if it means fighting the supernatural at every turn.