Natsuki Books was a tiny second-hand bookshop on the edge of town. Inside, towering shelves reached the ceiling, every one crammed full of wonderful books. Rintaro Natsuki loved this space that his grandfather had created. He spent many happy hours there, reading whatever he liked. It was the perfect refuge for a boy who tended to be something of a recluse.

After the death of his grandfather, Rintaro is devastated and alone. It seems he will have to close the shop. Then, a talking tabby cat called Tiger appears and asks Rintaro for help. The cat needs a book lover to join him on a mission. This odd couple will go on three magical adventures to save books from people who have imprisoned, mistreated and betrayed them. Finally, there is one last rescue that Rintaro must attempt alone . . .