When sixteen-year-old Ellie Baum accidentally time-travels via red balloon to 1988 East Berlin, she's caught up in a conspiracy of history and magic. She meets members of an underground guild in East Berlin who use balloons and magic to help people escape over the Wall—but even to the balloon makers, Ellie's time travel is a mystery. When it becomes clear that someone is using dark magic to change history, Ellie must risk everything—including her only way home—to stop the process.