Cassidy Blake's parents are The Inspecters, a (somewhat inept) ghost-hunting team. But Cass herself can really see ghosts. In fact, her best friend, Jacob, just happens to be one.

When The Inspecters head to ultra-haunted Edinburgh, Scotland, for their new TV show, Cass and Jacob come along. In Scotland, Cass is surrounded by ghosts, not all of them friendly. Then she meets Lara, a girl who can also see the dead. But Lara tells Cassidy that as an In-betweener, their job is to send ghosts permanently beyond the Veil.

Cass isn't sure about her new mission, but she does know the sinister Red Raven haunting the city doesn't belong in her world. Cassidy's powers will draw her into an epic fight that stretches through the worlds of the living and the dead, in order to save herself.