Sense and Sensibility and Sea Monsters! (Also available are Abraham Lincoln: Vampire Hunter and Little Vampire Women!)
Sense and Sensibility is a tale of two sisters Elinor and Marianne, who are looking for love. They've been kicked out of their family home due to them being girls and not boys so they're not doing so great. There are heartbreaks and romance, arguments and misunderstandings, happily the novel ends with them finding true love. Now take that and throw in an underwater city, an adventuring uncle, and random monster attacks.
Basically you're getting the story of S & S (with a few omissions that don't lend themselves to the new additions, an example is that instead of twisting her ankle one of the sisters is attacked by a giant octopus) with all-new scenes of giant lobsters, vicious jellyfish, two-headed sea serpents, and more! It's definitely silly-sea-monster-fun! Of course I can see where the Jane Austen purists are grumbling, to appease everyone the books should be sold as a two-fer, buy the Sea Monster one and get the original for free!
Here's the book trailer: