In a desolate, post-apocalyptic Mexico City, biological siblings Lucio and Fauna wander the ruins in a desperate search for food and shelter. They stumble upon a massive, decaying industrial building inhabited by Mariano, a bizarre and charismatic madman who offers them a means to survive. In exchange for refuge, Mariano forces the brother and sister to help him construct a surreal, cavernous womb-like structure inside the warehouse. As they become completely isolated from the outside world, Mariano systematically breaks down their moral defenses, pushing the siblings into a dark psychological descent where they abandon societal taboos to engage in extreme acts of biological incest, violence, and primal ritualism under his watchful eye.