This book was written for kids like me: the puzzle-solving, mystery-loving logicians. I love that there was a mini-mystery for the reader to solve (the message hidden in the illustrations), and I like the incorporation of pentominoes. I also think it very effectively educates the reader about art.
However, it was too much. By the middle of the book, I got the illustration code (ok, so maybe it was directed toward a younger audience) and I was ready for the mystery to be solved. There were too many coincidences and patterns and dreams and imaginary links for it to be believable: 12-12. The pentominoes in Calder's pocket signifying a particular word clue. Petra's dreams. The pocket of Vermeer lovers in that 3-block neigborhood. Glitt marrying the mother of Calder's best friend. I stopped paying attention after a while, and just wanted them to solve it, because I knew I had no hope of sifting through what was real and what wasn't.
See, as a student of logic, I know that dreams are not prophesy, and random letters can signify anything you want.
It bothered me that Calder kept the pentominoes in his pocket. The whole collection seems big enough to prohibit that.
The book also seems to break the rules of mystery novels. We don't know the thief at all, when usually the thief/murderer is hiding under our noses the whole time.