"I'm never stocking them again, never! It's been bedlam! I thought we'd seen the worst when we bought two hundred copies of the Invisible Book of Invisibility — cost a fortune, and we never found them."
The Invisible Book of Invisibility was a textbook about the power of invisibility. As the manager of Flourish and Blotts told Harry Potter in 1993, at some point in the past, Flourish and Blotts ordered a stock of the book, only to have all two-hundred of them disappear, and no one was ever able to find them, costing the store a fortune. Only the stock of The Monster Book of Monsters was considered more troublesome. "The Invisible Book of Invisibility" most probabbly teaches invisibility spells as well as theory.