Everyone in Whispering Pines knows their town is full of ghosts, but Helena Novak hasn't seen a trace of her late grandmother, Babi. Helena and her best friend, Ben, spend most of their free time in the cemetery, yet no amount of gifts on Babi's grave has lured her spirit out. But someone else has been paying attention.

Helena feels she's being followed, and one day, all Babi's grave gifts disappear. When Helena and Ben investigate, they find a secret door in a crypt that leads to the underworld itself. The sprawling subterranean world is a maze of eerie kingdoms, piercing castles, creepy forests, swirling seas, and crowded marketplaces full of unsavory characters. While the living can visit, if they get lost--or taken by the mysterious Nightmare--they won't be able to leave. Despite the danger, Helena is set on finding her grandmother and seeing for herself that Babi is doing well in this strange place.

So when eccentric underworld guide Grumbones offers to help Helena and Ben find their way, they think it's their lucky break. Sure, he looks like Santa's skinny evil brother and some of the memento mori spilling out of his pockets look awfully familiar, but better a slightly suspicious helper than none at all...right?