Perfectly good adventure; would have loved it as a kid. The care that went into describing and thinking about the puppets – made from wood, metal, paper, and having different professions and skills and life spans – was typical Tchaikowsky. The book felt a bit rushed to me, but I think that’s just very good middle-grade pacing: make all the things happen all the time! Good book, even though it made me feel my age a bit.
Beware: full spoilers! Also probably incomplete and possibly incomprehensible.
Coppelia makes puppets with her magic, mostly in service of a small-fry villain in her magically oppressive city. But there are also real live puppets, and she helps them out by making more of them (though she’s very much not the one calling the shots). They dare to go into the inner city and find out that the archmage himself has moved his consciousness (or actually, plot twist: not) into a bit fancy robot. Adventure ensues, until she breaks the evil oppressive faux-magician robot.