The first thing I have to say is that you really need to read all three of Julia Jones' "Strong Winds" trilogy in the right order. I'm not sure how well this would work as a stand alone book. That may sound like a criticism but it's not meant as such. Just that it would be like reading "The Return Of The King" on its own, without the benefit of the synopsis at the beginning of Tolkien's third volume.
This is another white knuckle ride which kept me reading late into the night. All is explained as far as the back-story of the leading "Goody" characters is concerned, and a pretty satisfactory resolution arrives. (The tributes to Arthur Ransome come thick and fast, too.) If I'm not quite able to give it the fifth star it's because I think the mechanisms by which the "Baddies" work their wickedness are not fully explored or explained, and their come-uppances are just a bit perfunctory. I may be old-fashioned, but I wanted to know how they are going to suffer (and I wouldn't have minded seeing them suffer more)! I don't think that the filling-in of these lacunae would necessarily lengthen the book overmuch.
That said, I have loved this series of books. They are contemporary, liberal-minded, fast-paced, and a realistic reflection of early teenage life in the often hostile environment of a target-driven Secondary School and in the clutches of overstretched Social Services. And - above all - they are humane. The artwork is great and the production values are as good as any I've seen in a paperback. I'd buy all three for any teenager who reads - and I will buy them for my sons - who are considerably older!