It's been about three years since the last book, and Piemur's voice is changing. Having lost his famous soprano voice, Masterharper Robinton decides it's time to put Piemur to good use with his other abilities. Piemur's primary other talents include picking up important snippets of information and putting them together to see the whole of whatever's going on, and dissembling. So Master Robinton secretly makes Piemur his new apprentice, and assigns him to the drumheights (the primary message center). This way, Piemur will be in a position to send and recieve messages, as well as covertly perform any other tasks the Masterharper might wish.
This is my least favorite book in the Harper Hall trilogy. I like Piemur, but as the other two books are about Menolly, I would have expected her to be more important in this book than she actually turns out to be.