Young Paolina Barthes, a gear-minded prodigy and target for the empire-building ambitions of rival governments, is on the run, heading south over the Wall that God built to divide the hemispheres and keep the Earth's gear turning through the heavens. As spies and ancient secret societies scramble to find her, Paolina struggles to learn how to control her world-shaking abilities, while her heart pulls her toward Boaz, a golemlike man of brass.