Unless you're belted in, there's no way you're hanging on.

Back cover:

Keston Ochiltree's visit home had been short and disastrous. His newborn nephew had proved to be one of the Hopeless Ones and had only served to remind him of the present plight of mankind. Keston knew that the decision he was being called on to make might mean a new start for humanity or the end of their underwater civilization.

Should he stay in the Emperor's shark-cavalry to fight the Zammu?

If you're 14, such issues matter. Otherwise you might pause, look up from the pages, and think "I am wondering about the shark-cavalry going up against the Zammu. My life has thus far been spent for naught."

I mean, I'm all for flights of fancy and imaginative stories, but I'm at the age where underwater emperors commanding legions of shark-riding humans seems something of a stretch.