What if man journeyed into space in 1869, not 1969? In search of the mysterious element known as aether, Claire Dulac flew her hot-air balloon toward the edge of our stratosphere-and never returned. One year after her disappearance, her son and husband are delivered a tantalizing clue: a letter from an unknown sender who claims to have Claire's lost logbook. The letter summons them to a Bavarian castle, where an ambitious young king dreams of flying the skies in a ship powered by aether. But within the castle walls, danger lurks-there are those who would stop at nothing to conquer the stars.