As the city that produces the most selium - that precious gas that elevatesairships and powers strange magic - Hond Steading is a jewel worth stealing.To shore up the city’s defenses, Detan promises his aunt that he’ll recoverNouli, the infamous engineer who built the century gates that protect theimperial capital of Valathea. But Nouli is imprisoned on the Remnant Isles, animpervious island prison run by the empire, and it’s Detan’s fault.Detan doesn’t dare approach Nouli himself, so his companions volunteer to getthemselves locked up to make contact with Nouli and convince him to help. NowDetan has to break them all out of prison, and he’s going to need the help ofa half-mad doppel to do it.