The Flying Fish is an airship/submarine of extremely advanced technical prowess. Four gentleman adventurers who happen to meet more or less by accident set out aboard her to have adventures and claim what might be claimed in the name of dear old England. They visit the bottom of the English channel, the North Pole, various locations in Africa, Mt. Everest, the Indian Ocean and whatnot. Classic adventure fiction of the day.
The plot meanders through a series of episodic adventures then stops without ever achieving much of an overarching anything. The prose, by modern standards, runs to the dreadfully purple, though still quite readable and entertaining in its way. The technology and other skiffy bits range from pleasingly convincing to ridiculously laughable.
The embedded cultural assumptions are amazing, to the point of feeling ridiculously stereotyped. For instance, there's an entire chapter of one character lecturing the others on how greedy and foolish laborers have through the evils of unionization caused the poor investors to be unable to realize the appropriate return on their capital, and why this is driving jobs out of England. Upon discovering a herd of unicorns, the characters grab their guns and go unicorn-hunting. The East African sequence late in the book is an appalling example of colonialist literature — cringe-inducing almost beyond measure.
Still and all, this is steampunk in the original Klingon. If you want to read Victorian adventure set aboard a fantastic and impossible airship, as written by a Victorian adventure writer, Collingwood is your man.