The Knights of Mars -|Castle in the Stars, Bk. 3|-

What if man journeyed into space in 1869, not 1969?When Seraphin, Hans, and Sophie returned from their voyage to the moon, they didn|t come home empty-handed - they brought with them aetherite, a miraculous substance that defies gravity! To keep their secret safe from the Prussians, the trio lives in hiding on a remote island in Brittany. Meanwhile, Seraphin|s father has founded the International Society of Aether, a group of scientists dedicated to the peaceful pursuit of space exploration. But on the eve of their inaugural meeting, he vanishes without a trace!The Knights of Aether|s last hope lies in a daring rescue of King Ludwig and Professor Dulac. They will find them on the farthest outskirts of the Prussian empire - the planet Mars!