Mysterious letters delivered after dark, showers of frogs, and unexplained repetitions of the number 12 are just a few of the diverse elements present in this intricate mystery. Sixth graders Calder and Petra, classmates both hovering on the fringes of their school’s social scene, are drawn together by a missing Vermeer painting. Petra is sensitive to words, while Calder operates comfortably within a world of symbols and patterns. Both children bring their unique skills and perspectives to the search for the lost painting, and together they make a formidable detective duo. As events escalate to a frenzy (often playfully stretching credibility), readers are invited to share in the sleuthing process. In addition to hints and clues within the story, images of pentominoes are camouflaged within the illustrations, offering a hidden message if correctly decoded. Ultimately, Petra and Calder’s resolve pays off as they solve the mystery and raise some important questions about art, friendship, perception, and truth along the way. (Ages 9–12)