From Mo Willems, creator of the revolutionary, award-winning, best-selling Elephant & Piggie books, comes this breakout beginning-reader series. An ensemble cast of Squirrels, Acorns, and pop-in guests host a page-turning extravaganza. Each book features a funny, furry adventure AND bonus jokes, quirky quizzes, nutty facts, and so, so many Squirrels. In Who is the Mystery Reader?, Zoom Squirrel tries out a new superpower with help from a mysterious Mystery Reader. But will the Squirrel pals ever find out who the real Mystery Reader is? Do you know more about reading than the Squirrels do? You will by the end of this book! Editorial Reviews 10/01/2019 K-Gr 2--The gang from I Lost My Tooth is back in three episodic vignettes tied together by squirrels, puns, and acorn jokes. A group of squirrels halts before a red octagonal sign because they cannot read it. A squirrel enters wearing a red mask and underpants. He is the Mystery Reader and shows the other squirrels how to sound out words. Silliness follows as the squirrels try to figure out the Mystery Reader's identity (insert a joke told by anthropomorphized acorns). In the next sketch, Wonder Squirrel wonders what the first writing looked like. This is followed by actual facts about cuneiform and hieroglyphics. And another acorn joke. In the third sketch, two squirrels want to know how they got into the book and are told the story about Mo Squirrel and how ideas become a book. The concepts are a bit more sophisticated than Willems's previous series titles and the factual material is a higher reading level than the rest of the book. Still, the mashup of stories is oddly cohesive and has the feel of an animated cartoon. VERDICT Willems's fans will enjoy this offering. After all, who can resist a squirrel in underpants?-Kelly Roth, Bartow County Public Library, Cartersville, GA - School Library Journal 2019-07-24 The Unlimited Squirrels return for a metafictive romp--hooray! Carrying a copy of the book (yes, this book), one squirrel asks "Who is the MYSTERY READER?" The others respond, one after another: "Let's. Read. And. Find out!" So begins this sequel to I Lost My Tooth! (2018), a brilliant, 96-page laugh track composed of four stories and three "acorn-y" jokes. In the first story, the squirrels struggle to decode the letters of a stop sign. Thankfully, the heroic Mystery Reader arrives on the scene--complete with mask and underpants--to help them sound out their letters: "Ssssttt... / ...OP!" The second story includes a brief history of writing systems (and a web address for further info); the third divulges "Mo Squirrel's" own writing process. Though narratively all over the place (in a good way), this takes the self-referential torch from We Are in a Book! (2010) and highlights the next step up in reading development. Willems' high-interest presentation and formula create a familiar, entertaining format that combines fact, fiction, and plenty of squirrels. The text complexity is similar to that found in the Elephant and Piggie books, but there are more color-coded dialogue bubbles per page. Willems also employs "emote-acorns" to highlight characters' emotions. Readers may never find out who the Mystery Reader is, but, in the process of investigating, they just might sound out their own reading superpowers! Delightfully on-brand. Kids will book it to the shelves for this one. (Early reader. 5-8) - Kirkus Reviews