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.

Trouble is haunting Cassidy Blake . . . even more than usual. She (plus her ghost best friend, Jacob, of course) are in Paris, where Cass' parents are filming their TV show about the world's most haunted cities. Sure, it's fun eating croissants and seeing the Eiffel Tower, but there's true ghostly danger lurking beneath Paris, in the creepy underground Catacombs. When Cass accidentally awakens a frighteningly strong spirit, she must rely on her still-growing skills as a ghosthunter—and turn to friends both old and new to help her unravel a mystery. But time is running out, and the spirit is only growing stronger. And if Cass fails, the force she's unleashed could haunt the city forever.

Where there are ghosts, Cassidy Blake follows ... unless it's the other way around? Cass thinks she might have this ghost-hunting thing down. After all, she and her ghost best friend, Jacob, have survived two haunted cities while travelling for her parents' TV show. But nothing can prepare Cass for New Orleans, which wears all of its hauntings on its sleeve. In a city of ghost tours and tombs, raucous music and all kinds of magic, Cass could get lost in all the colourful, grisly local legends. And the city's biggest surprise is a foe Cass never expected to face: a servant of Death itself. Cass takes on her most dangerous challenge yet...