Escape from Mr. Lemoncello's Library by Chris Grabenstein

...Did he mean to name Sierra....Sierra.... The book nerd.... But unlike one Sierra I know, I love this one, and she's super helpful and friendly.
You can't just mention underwear multiple times and expect me to not think it's a clue.
....It's not if you consult the internet for help about the final clue that wasn't in the book, right?

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