Three thousand years ago, Dayu sealed the strange beasts of the mountains and seas and engraved their names into the "Book of Mountains and Seas"; three thousand years later, the seal was loosened, gluttons devoured cities, Gu eagles cried in the moon, and the human world became a hunting ground for strange beasts. Su Yan, an ancient book restorer, accidentally awakened the guardian spirits of the mountains and seas in the book, and was forced to embark on a journey to complete the fragments. He needs to traverse the thousands of rivers and mountains recorded in the book, persuade the alien beasts who are unwilling to return, and fight against the mysterious organization that attempts to tamper with ancient books and subvert the three realms. On the way, he is paired with the heir apparent of the Xuannio clan who bears a blood feud, struggles between trust and betrayal, and glimpses the truth of the ancient divine war on the verge of life and death - it turns out that what the bookkeeper guards is never the classics, but the balance of the coexistence of humans and strange beasts.
