The Tinkerers

"When Peter leads two Tinkerers to his family's inn in Stargazers Valley, he imagines they're like other astromancers, researchers from the Imperial College who study starstuff. The valley is a special place, where the magical aurora called the Skeins appear in the sky and starstuff falls in their wake, as thin and wispy as fluff from a seed pod. But starstuff is powerful, and astromancers are the only people allowed to handle it -- a law enforced by the strict and stealthy Outbounder Task Force. When Peter discovers the Tinkerers have used starstuff to invent an incredible not-a-clock that can turn back time for a few minutes, he realizes it's his chance to undo his mistakes: if he can go back and put away his new boots, he doesn't need to add their destruction by falcons to his list of ten worst mistakes (#7: stepping on a star-eating newt). But while using the not-a-clock is easy, stopping using it is hard. And maybe not everything that feels like a mistake at the time actually is"--