A perpetual drifter, Kier Templer lives her life on the road. Dubbed "the monster's daughter" after her mother's infamous crime, Kier has left her hometown and twin behind. Kier is haunted by the past, but one thing has always bound her to her brother, Penn: the distinctive maps she designs of the places she's explored. When Kier abruptly goes off-grid without sending him her latest, Penn knows something is seriously wrong.

Elin Warner is on vacation with her brother Isaac in a rugged national park in Portugal--the last place Kier was seen. It's supposed to be a time for the siblings to reconnect, but when Elin discovers Kier's disturbing final map, it seems the park--especially the inhabitants of a camp buried deep in the forest--holds clues to what happened to Kier, and a lot more besides.

After a sinister discovery, Elin is shocked to learn Kier's disappearance is more personal to her than she'd ever imagined. And as she seeks the truth, Elin soon finds the wilderness hides something far darker than shifting shadows...