"The Sea of Monsters" is book two in the series "Percy Jackson and the Olympians." If you missed the review on the first book that I did, go here to read it!
In book 2 we rejoin Percy at his new school towards the end of the school year. He's had a pretty easy school year for once, no monsters attacking, but of course he can't make it through the entire year free from torment. A "friendly" game of dodge ball turns into a deadly attack, and to Percy's surprise, he finds his friend Tyson protecting him way more than he should be capable of. It turns out Tyson is more than he appears to be!
Soon Percy discovers that Camp Half-Blood is in trouble, as is his friend Grover. The solution to both problems lies in the legendary Sea of Monsters. It, like the gods, moved location with the change of power, and is now located in the Bermuda Triangle. So, of course, he goes off on a new quest to save Grover, and Tyson goes along.
Percy grows up a lot in this book. He learns more about his "family" and about who he is as a person. Does he save the day? Well, you'll have to read the book to find out!