After human civilization collapses, the last remaining Apocalypse Fortress is besieged by gray-green bone-corroding fog and four factions of gods, demons, monsters, and ghosts, becoming humanity's final line of defense. Quan Nanzhu, an “outcast” rejected by the fortress, has mysterious nonhuman blood flowing through his veins, allowing him to sense the movements of monsters in the fog. Wang Ruyi, the daughter of a mid-ranking fortress officer steadfast in her belief in humanity's survival, is meanwhile scrambling to repair the defense wall on the verge of collapse.
During a sudden assault by the bone-corroding fog, the two cross paths by chance. Quan Nanzhu pinpoints the fog core with uncanny accuracy and is forcibly assigned to the exploration squad led by Wang Ruyi, becoming its “special consultant” in the search for the core. The squad includes Lin Ye, a mechanical craftsman who joined because his younger sister was infected by the fog, and Zhao Chengying, a former subordinate of Wang Ruyi's father who is actually an informant for the conservative faction.
As they venture deep into the Forest of Bones, they encounter Qing Li, a young fox demon clan leader coerced by the ghost clan. They are drawn into a conflict in the buffer zone between the gods and demons, taken into custody by Xuan Zhen, captain of a divine patrol, and repeatedly hunted by the ghost clan's envoy, Black Impermanence. As their exploration progresses, the truth behind the ancient “Pact Between Humans and Gods,” the secrets beneath the fortress, and the connection between their origins gradually come to light. They are searching for more than the fog core: they seek the “Rift Key,” which can reshape the balance of power among the factions. Behind this key lie the source of humanity's apocalypse and the possibility of breaking the cycle.
Factional infighting within the fortress, brutal struggles among the factions, and the collision between nonhuman blood and human conviction push the pair to the brink of destiny. From mutual rejection to trust, Quan Nanzhu and Wang Ruyi must choose between holding fast and giving in to doubt: will they protect the tottering human
