Thirteen-year-old Nanami loves to read and happily spends much of her free time in the library. Despite the library being as deserted as ever, one day she notices that some of her favorite books are disappearing from the shelves. Then she spots a suspicious man in a gray suit and follows him. The chase is cut short when Nanami suffers an asthma attack. By the time she catches her breath, the man has disappeared, and all that is left behind is a mysterious light filtering through the library’s familiar passageways. That’s when Tiger, the talking tabby cat who saves books, comes to the rescue. Are Nanami and Tiger prepared to face the dangerous challenges that lie ahead? Why are faceless gray soldiers burning books in a stone castle? And what happened to Rintaro, the socially withdrawn hero who helped Tiger save books in a second-hand bookshop?

Bookish high school student Rintaro Natsuki is about to close the secondhand bookstore he inherited from his beloved bookworm grandfather. Then, a talking cat appears with an unusual request. The feline asks for --- or rather, demands --- the teenager’s help in saving books with him. The world is full of lonely books left unread and unloved, and the cat and Rintaro must liberate them from their neglectful owners. Their mission sends this odd couple on an amazing journey, where they enter different mazes to set books free. It all culminates in one final, unforgettable challenge --- the last maze that awaits leads Rintaro down a realm only the bravest dare enter.