Book 7, and the conclusion, of the Septimus Heap series. A lot of threads are tied together here, so spoilers ahead for the first six.
It opens with a flashback to the days of the first queen, and the origin of the Two-Headed Ring. Back in the usual time, Simon and Lucy's wedding is a grand occasion, and Marcia, despite her oath to abjure all things Alchemical, has agreed to let Marcellus restart the Fyre, so they can denature the Two-Headed Ring, and even let Septimus act as his apprentice for a month. The chamber's quite an impressive mess -- but he's not showing her the real thing.
Meanwhile, the Dragon Boat is sickening, and Aunt Zelda is growing senile.
The story weaves on involving a messenger rat in training, an old smugglers' route, memories from being a cook, snowmen, a vacation for Septimus, a discovery about an old disaster, preparations for the coronation, a last attempt to steal the princess by a coven -- queens aren't any good -- and a long journey to a city that is not given a name, but looks kinda familiar.
It is also established quite definitively that it is the far future.
We are explicitly told who's going to have the next series in the last of the "what happened after" tidbits. Not one you might expect. I hope to see some reappearances, because some threads were kept hanging -- mainly romances.