Michael Dahl 
Last Word [PDF ebook] 

In the heart of the Library of Doom, within the Librarian’s secret chamber, is a sealed, invisible vault. It contains a single book — a book so poisonous that it drains the Librarian’s life away day by day, year by year. It is the price each Librarian must pay, because if anyone reads the final word in the story, the whole world will be destroyed! So when the book goes missing, the Librarian must track it down without delay. There’s just one problem: only another Librarian would know where the book was located . . . Is there a traitor in the League of Librarians?