Pathfinder, came out this October (from Katherine Tegen Books).
All the things that I enjoyed about the Septimus Heap books are here in Pathfinder (including the appealing illustrations--I mostly don't look at illustrations, but I do for these books because of liking them. They are the sort of pictures that one can imagine drawing of the people in ones own imagined world).
There's the really large cast of characters to care about (with the added bonus of lots and lots of old friends). It is true that it would be hard to keep everyone straight if you hadn't read the first series, but I think it would be doable. There's the very appealing hero of the story, in this case a girl named Alice Todhunter Moon (who likes to be called Tod). Tod is special, but not Chosen; she's brave despite being frightened; she's a good friend and likable person who just happen to have a strong talent for Magic.
And there's a story with lots of twists and turns and bits and pieces that all comes together by the end of it (at least I think they all came together, but I was reading for character not plot so can't promise there weren't plot holes), and which I am not going to recap because it would take too long and because I think my attempts to do so would not convince anyone to read it who didn't already want to. If you loved Septimus Heap, read this too. If you were unsure about S.H., read this one anyway because I think there is a bit more tightness to it, and it's a faster read. If you have never read any S.H. books, but want a satisfying story in a richly imagined world, full of people who care about each other, give it a try.
Here's what I admired most about this book, though-- it starts a new series with new additions to the world, making it a fresh and interesting story while at the same time continuing the stories of what the old friends from the first series are up to. I was very pleased.
In large part because I really did like Tod a lot.
Thing I didn't like--I never find it appealing when there are people who get gills. I think gills are gross. Just saying.