Sol and Felix, a married couple, take their two children, Sara and Adolfo, on a family outing to the hills near Tijuana. During their excursion, Sara and Adolfo wander off to explore a secluded cave, leaving Sol and Felix behind. The parents soon realize the children are missing and frantically search for them as night falls. Despite their best efforts, they can’t find the children and reluctantly return to their motel, hoping for their safe return. The next morning, Sara and Adolfo reappear, seemingly unharmed but exhibiting unusual behavior that worries their parents.

As time passes, Sol and Felix notice increasingly disturbing changes in their children's demeanor. They consult doctors and even delve into local folklore in a desperate attempt to understand what might have happened during the children's disappearance. Their investigation leads them down a dark path, uncovering terrifying truths about the area’s history and its sinister forces. The once-close-knit family finds themselves grappling with an intensifying nightmare that extends beyond their understanding, threatening to consume them entirely.