The underwater library, hidden in the depths of the earth under Tokyo Station, stores rare books from all over the world. It is here that all the world's art dealers come, experienced in the expert assessment of ancient books and manuscripts, because only here you can sell and buy the rarest publications. Victory at the auctions goes to the one whom Goshiki, the Head of the Library, recognizes as the “suitable” owner for the lot: a fierce struggle unfolds for each of them. Librarian Mimori, although unable to refuse anything to his friend Shu, a hunter for antiquarian books, regularly protects library collection from scammers and international criminals. But one day the unexpected happens. Someone is attacking the Head of the Library...