Which book is missing from the series? :-) Picture by awinn233

Question:  Every wondered what book 26 is in the Geronimo Stilton series? 

Answer:  The Mummy with No Name

An easy place to find the answer is right here. 

A library in Missouri has organized tons of series!  It's pretty awesome; it contains over 29,000 children's books.

You can also use the database Novelist.  Find children's books similar to other books, their descriptions, and reviews of them too.  Have your library card handy.