Not long after the earthquake that brought the four of them together, Sandry, Tris, Daja, and Briar find themselves involved in another dangerous situation.  While they continue to learn about their magic, they now have to deal with a massive pirate fleet seeking to invade the Winding Circle with magic and a powerful new weapon.  Despite the temple's own powerful defenses, it looks like it'll be a battle of attrition if something isn't done to swing things in the temple's favor.

Tris' Book is the second book in the Circle of Magic series, and it really ups the stakes from the last one.  Whereas Sandry's Book mainly focused on the four children as they find a place where they belong and learn about their magic, this one had an actual villain to deal with.  The main characters are still learning their magic, but that winds up having to take a backseat due to the events in the story.

I highly recommend these books to anyone who wants to read a good fantasy story.