The Pinhoe Egg. by Diana Wynne Jones

Dianna was a genius with pen and paper as far as I'm concerned. (I use the word 'was', because sadly she passed away last year.................... A moment of quiet in respect.....................)

I have yet to read one of her books that I didn't like, and 'The Pinhoe Egg' is my favorite of the lot. 

Hmm, I'm having trouble describing what I liked about it without giving away spoilers, so I'll start by saying the simple things and hopefully that will put some wind in my sails.

• It's aimed at a younger audience, but it's enjoyable for everyone.
• Her writing stile is simple but engaging. It has a steady rhythm to it that manages to remain constantly "new" yet not overwhelming. 
• It's part of the Chrestomanci series about Chrestomanci who is a very powerful enchanter, who's job it is to police other magic users so that the don't misuse it.
  'The Pinhoe Egg' is about Erik Chant - aka Cat - who is in training to be the next Chrestomanci.

I would definitely recommend it to anyone. 

And that's pretty much all I can say about it I think without turning this into a spoiler version.