Can a sculpture move? If it's a Alexander Calder mobile, it can.

Petra, Calder and Tommy were convinced it was going to be a terrible year. They were in the seventh grade now, and had a new teacher, Ms. Button. She was serious about everything, she was sure she knew everything, and she didn't answer questions. She was the exact opposite of Ms. Hussey, who'd been their sixth grade teacher.

Even a trip to the Museum of Contemporary Art, to see a huge exhibit of Alexander Calder's mobiles, wasn't fun, because they couldn't talk, or point, or touch, or get out of line, no matter what. But the mobiles could get out of line, and they did, dancing and spinning, making new patterns. Calder saw them as mathematical equations, like his pentominoes, Tommy saw them as a way to create beauty with his found objects, and Petra saw them as three dimensional sentences, floating and changing constantly.

They didn't know that there was someone watching them, a man who saw their excitement, and who also saw how Ms. Button squelched it with a single word. That same man followed Calder when he slipped away to play the Calder Game. "Take five pieces of paper and create your own mobile, with balance, beauty and surprise." He saw Ms. Button refuse to let the class visit the game room, and then went back to the exhibit, to stare at a small mobile of black wedges. No one paid any attention to him when he suddenly got up and walked away. No one noticed the small piece of paper that fell out of his overstuffed folder. There were four words on the paper-"Hunt for Creatures," and under that, "Hang."

The pieces of the mystery were coming together, forming patterns. Calder, his father, and their trip to England were one piece, the Calder sculpture of the minotaur was another, and its disappearance on the same night Calder disappeared was yet another. The secret that Ms. Hussey told Calder when she learned he was going to England was a piece, and so was Petra's and Tommy's trip to England to find Calder. The man at the museum and his lost scrap of paper were a piece of the mystery — could they be the key piece, the one that made all the other pieces change their directions and form new patterns?

There's more to see in a Calder mobile than first meets the eye. A missing boy, a missing sculpture, and the mystery that links them together are as simple and yet as complex as one of Calder's beautiful, ever-changing mobiles.

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