The Bell, the Book, and the Spellbinder — John Bellairs

Hidden away in the local library, a sorcerer’s book casts an evil spell in a novel by the author of The House with a Clock in Its Walls
 
Johnny Dixon and his best friend Fergie are whiling away a rainy day at the Duston Heights library when Johnny asks a screwy question: “What’s the last book in the library?” After Johnny goes home, Fergie decides to find out. There, under number 999.99, he finds a very peculiar tome, The Book of True Wishes, which is all about Fergie’s favorite subject: himself. The book knows Fergie’s name, and it promises him everything he ever wanted, which means he is about to forget a very important rule: Be careful what you wish for.
 
When the book puts Fergie under the spell of a mad old wizard, Johnny and his friend Professor Childermass will do whatever it takes to break the book’s hold and save their friend.
 
Johnny Dixon and his eccentric professor friend are two of the most delightful characters in literature as well as “an endearing detective team,” and their adventures continue to hold readers of all ages spellbound (The New York Times).