Nicholas, or Nick, Vargas is upset. His mom died long ago, and his dad recently remarried, saddling him with a stepsister named Laurie. When they moved into a new house together, Nick lost his old room and now has to share one with his brother, Justin, who snores very loudly. Nick's old room went to his new stepsister, and Nick thinks she's a weirdo. After all, she's into unicorns and fairies and everything in her room seems to be covered in glitter, have unicorns or fairies on it, or some combination of all three.
Worst of all, his father wants him to get along with Laurie, so he feels compelled to go outside with her and explore. Laurie tells him she's looking for fairies or a four leaf clover. Nick quickly gets bored with this, but actually does find a four-leaf clover. At first, he thinks of giving it to Laurie, but decides that he needs the luck and keeps it for himself before abandoning her and returning to the house when it starts to rain, to play video games.
Later, the rain gets heavier, and the power goes out. Nick spots a body lying in the grass, and, feeling afraid that it might be his new stepsister, goes out to investigate. But it's not Laurie. It's a mermaid, and the only reason he can see it is because of the four-leaf clover he found. He and Laurie take the mermaid's still-living body to the pond and dump it in, but he gets in trouble for using his father's wheelbarrow to move the body, and blames Laurie for it.
Soon, Nick is caught up in the Mermaid's demands to find her sisters, and dealing with a fire-breathing giant that he accidentally awakened. Can they find some way to deal with the giant before it burns down the entire building development around them?
A follow-up to the original five Spiderwick books, this does a good job of expanding the franchise and moving the action from the northeast to the southeast, in this case, Florida, and introducing new foes and fairies for the protagonists to encounter. The authors also fall prey to the temptation to write themselves into the book, although what help they give the protagonists is... well, you'll have to read for yourself to answer that one.
This series is a wonderful follow-up to the original, and any readers who enjoyed the first will find just as much to enjoy here and more. A recommended read.