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Orange_Cat_155 thinks this title is suitable for 11 years and over
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Calder and Petra are 6th graders in Chicago. Petra loves words; Calder is more comfortable with math and puzzles (like the pentominoes he carries with him everywhere). Three anonymous letters, a mysterious book, and a stolen Vermeer painting make Calder and Petra join forces. They work together as clues and puzzles lead them further into the mystery. Readers are encouraged to work out the puzzles (decoding messages, math puzzles, etc.) along with Petra and Calder.
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