Hans Christian Anderson's The Little Mermaid is a horribly depressing story. Jim Hines takes that story and makes it even more horrifying. So yet another princess missed out on her 'happily ever after'. Only this time the princess strikes back. Against those who hurt her and those who want to help her.
The Mermaid's Madness begins with the Lorindar nobles welcoming the return of the undine (merfolk) from their annual hybernation. Only this time the undine aren't happy to see the humans. The subsequent attack lands one noble greviously wounded and embroils Danielle, Talia and Snow in an adventure with consequences none of them are ready for.
The novel is fast paced, with well defined characters. Readers who haven't read The Stepsister Scheme will be confused by one or two points left unexplained from the first book, but won't otherwise have any trouble reading this book on its own. The true joy of this series is figuring out how Mr. Hines has twisted otherwise familiar (or not, depending on the version you read as a child) fairy tales. And this one is twisted indeed.