Claus and Lavie work as aerial couriers aboard a small flying craft inherited from Claus's father. They dream of crossing the vast storm known as the Grand Stream. A delivery involving a mysterious girl and the battleship Silvana pulls them into the struggle between their world's powers.
Their ambition carries a family history: their fathers could not complete the storm crossing. Courier work gives them the practical skill to fly while leaving them vulnerable to the demands of the people who hire them. Escorting Alvis changes the meaning of a delivery from paid work to a dangerous responsibility.
The early aerial battle has rules and even an arbiter, the Guild. When an attack breaks those rules and the Guild lets it pass, Claus and Lavie's civilian work enters a conflict whose supposed safeguards cannot be trusted. Completing a delivery now means dealing with the decisions of people commanding whole fleets.