The story revolves around Claus Valca and Lavie Head, a young courier pilot and his navigator, and their adventures in the floating world of Prester. In this romantic sky world based on stylized Victorian fashion and society, two countries, Anatole and Dysis (sometimes phonetically rendered as Anatoray and Disith), are engaged in a long and bloody war under the supervision of the mysterious Guild. Claus and Lavie, piloting their vanship (a small wingless aircraft) find themselves involved in a plot surrounding a mysterious little girl named Alvis Hamilton, whom they must deliver as "cargo" to the much-feared neutral battleship "Silvana".