Thirteen-year-old Nanami Kosaki finds comfort and friendship in the books at her local library. When titles begin disappearing from the shelves, she notices a suspicious man in a grey suit and considers following him. Tiger, a talking tabby cat, warns her that the pursuit could be dangerous, but they join forces to discover what is happening. Their search leads them along a frightening trail and tests Nanami's courage as they try to find the missing books. Through their adventure, the novel explores the importance of literature, independent thought and the willingness to question persuasive authority. It returns to the world of Tiger from The Cat Who Saved Books.