Romulus Buckle and the Luminiferous Aether (The Chronicles of the Pneumatic Zeppelin)

Earth is an icy wasteland, devastated by an alien invasion hundreds of years before. Left with only steam power, the human survivors have formed into steampunk clans. And now these clans are at war. Reeling from a Founders clan invasion, Captain Romulus Buckle of the Pneumatic Zeppelin faces a desperate decision. Does he return home to bolster the Grand Alliance or attempt to rescue his sister, Elizabeth, who is prophesied to be the key to winning the war? With only an ancient automaton and the words of a madman to guide him, Buckle leads an expedition to the mysterious underwater city of Atlantis, where mythical monsters and human treachery make every move perilous