The Dashwood sisters, Elinor and Marianne, live with their widowed mother and younger sister Margaret in Devonshire following the death of their father, who was mauled by a hammerhead shark. The seas have become dangerous ever since the mysterious and horrifying Alteration that has caused all the creatures of the ocean to become vicious and violently opposed to humans, and the sisters have had to train to defend themselves against attacks from the waters all their lives. Elinor has an on-again, off-again flirtation with the seemingly oblivious scholar Edward Ferrars, who is seeking to figure out what caused the Alteration to begin with, when the family is forced to move to a chain of islands owned by Sir John Middleton instead. There Marianne falls hard for the dashing explorer Willoughby, while simultaneously attracting the unwanted attentions of the older and dreadfully disfigured Colonel Brandon.
Contains examples of:
- Even Evil Has Standards - Dreadbeard will kill anyone without a second thought except Mr. Palmer, who saved his life when they were children.
- Failed a Spot Check: Frequently one or another young lady will be so distraught about her own romantic troubles that she will completely fail to notice sea monsters bearing down on herself, despite all shouted warnings.
- Humanoid Abomination - Lucy Steele, who is revealed to be a sea witch.
- Rescue Romance - Marianne finally reciprocates Colonel Brandon's feelings after he kills Dreadbeard.
- Summon Bigger Fish - Well, a bigger octopus in the Final Battle with Dreadbeard's pirates.
- That's No Moon! - That's no island - it's the Leviathan!