A Goodreads user asked Chris Grabenstein:

Any clues for the thirteenth puzzle?

Chris Grabenstein Pay attention to the books Mr. Lemoncello drops into his dialogue...and see what they all have in common!!!

Just wanted to let you know - this account is to help catalog what my 7 year old son reads - and he read Escape from Mr. Lemoncello's Library in 2 days and said it was AWESOME. Here is my question mark? (A proud mom)

Joechen asked Chris Grabenstein:

Nicholas asked Chris Grabenstein:

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