Walker Kane didn't believe in monsters ... Until they took his daughter.

Beneath the streets of Edinburgh, an ancient evil waits. Each year, the Grendsluagh-a prehistoric monster of insatiable hunger-demands a human sacrifice in exchange for the city's continued prosperity. A secret society known only as the Cabal has overseen this sinister ritual for centuries, binding Edinburgh to a grim legacy of terror.

When ex-military search and rescue officer Walker Kane's estranged daughter Emily is taken to sate the Grendsluagh's appetite, he plunges into a race against time through a treacherous underworld of danger.

Aided by a mythology-obsessed librarian and a daredevil urban explorer with secrets of her own, Walker and his makeshift team must face nightmares at every turn to reach Emily before she is devoured. The deeper they delve into Edinburgh's serpentine catacomb, the more their resolve is tested-by the mutated monsters of the volcanic depths and the violence of the Cabal.

To save his daughter, Walker will sacrifice everything-even his own humanity-in a heart-stopping confrontation with the monster at the heart of the labyrinth.

A stand-alone action-adventure horror novel from USA Today bestselling author J.F. Penn. Join the exploration into depths that were never meant to be disturbed. The secrets of the CATACOMB are waiting to be unearthed-if you dare.