Leviathan is a steampunk alternate history novel set in World War I, where the Central Powers use mechanical war machines called Clankers, while the Allied powers rely on genetically engineered living creatures called Darwinists. The story follows two main characters: Prince Aleksandar, a fugitive Austrian archduke who commands a walking battle fortress, and Deryn Sharp, a British commoner disguised as a boy to serve in the air service aboard the living airship Leviathan. Readers enjoy it for its fast-paced adventure, creative world-building, and the suspenseful dynamic between the two protagonists as they navigate war, discovery, and friendship.