In Portugal's national park, dark forests close in from all sides and only a few campers brave the loneliness.

It's easy to get lost out here, but when solo traveller Kier Templer goes missing, there are signs she was in danger before she even left her home in Devon. Detective Elin Warner is supposed to be off duty, until she discovers a troubling clue Kier left behind and becomes determined to track her down. But when the campsite closes ranks against Elin's questions, the isolation starts to turn sinister.