The young mages go to war. In the aftermath of a major earthquake, pirates have some to raid Winding Circle, intending to take the mages as valuable slaves. The four children of Discipline Cottage, with a particular focus on Tris, gather their magic together to help in the defenses and eventual battles. Tris gets a chance to face down many demons from her past, including the family who didn't seem to care for her until she showed herself valuable as a mage. Valuable in the worst way.

I think I regard these books as "Tortall Light." Meant for a slightly younger audience, with correspondingly younger characters, they have far less of politics and not much of romance or sexuality, compared with Tortall. There's a similar magical feel, to the extent that I'm always expecting them to cross over, but they remain individual universes. However, the difficulty of the reading material is quite similar, so if you're fine with reading up or down in age, you can jump between the two series with no problems. So long as you can keep them straight in your head!

In general, a recommendation for any fantasy lover looking for a more tween or YA focus. It may be a bit less popular with girl-averse readers, since it does have three girl main characters to one boy, but that's most of Pierce's books, really. She's an amazing author, and hopefully the gender-focused reader on either side can expand their horizons.