In 1862, daredevil balloon pilot Amelia Wren teams up with pioneering meteorologist James Glaisher to advance human knowledge of the weather and fly higher than anyone in history. While breaking records and advancing scientific discovery, their voyage to the very edge of existence helps the unlikely pair find their place in the world they have left far below them. But they face physical and emotional challenges in the thin air, as the ascent becomes a fight for survival.