On a family vacation, a couple’s son and daughter disappear while exploring a cave-riddled mountainside. The children eventually return home seemingly unharmed, but are withdrawn and devoid of emotion. The parents fear they have fallen prey to something inhuman — and that this dark evil has come home with them.

A married couple loses their children while on a family trip near some caves in Tijuana. The kids eventually reappear without explanation, but it becomes clear that they are not who they used to be, that something terrifying has changed them.