The quartet from the two quadologies is off-stage in this entry, but the girl found by Briar, Evvy, is off to the Battle Islands with Luvo, Rosethorn and a water temple initiate named Myrrhtide but nicknamed Fusspot by Evvy. Something is mysteriously killing plants, poisoning water and otherwise doing some damage on the island Starns. Turns out it is volcanic activity.
I'm about halfway through this. I didn't even know this book _existed_ until I saw it at Willow Books (see, this is what happens when I don't visit bookstores in person -- I've been waiting for the next Beka Cooper book but not keeping an eye out for other projects). It is an unalloyed and unexpected (in that I wasn't anticipating it for months but pleasantly surprised) joy. I'm sure there are people out there who don't love Tamora Pierce, so I guess they might not like this one too. She wrote it for audio, so if you love audio books, give this one a spin and tell me how it works for you. I'm reading it the old-fashioned way: on paper.