Boa Constructor: A Branches Book (the Binder of Doom #2)

"Something is stealing machine parts from all over Stermont, including a wrecking ball from a local construction site, and Alexander and his fellow monster hunters, Rip, and Nikki, fear that it is building a Stermont-smashing machine--so the friends must use the resources of the summer maker program at the library to stop this monster, and perhaps even solve the mystery of who is leaving monster trading cards where the Super Secret Monster Patrol can find them."--Publisher's description.