The Wizard's Promise: The Doomspell Trilogy (Book 3‪)‬

The final part of the Doomspell Trilogy.
The magic of all children has been released. Throughout the skies of Earth they swoop, crossing continents, changing shape, diving to the ocean depths and playing the deadly new spell-games.
 
Rachel bides her time, watching the skies for what she knows will happen - the invasion of the Witches. But when it comes it is not in the way anyone expects, and there is also a new enemy — the huge, terrifying Gridda-breed.
 
To confront them will require all of Rachel's and her brother Eric's skill and courage, as they embark on a journey that takes them to Ool, home of the Witches — a world where mountains move and breathe, the sun never pierces the clouds and the snows are alive.

Reviews
'The writing is atmospheric and the plot gripping, as the children battle against awesome forces.' Good Book Guide
 
'A fast-paced, gripping read.' Times Educational Supplement
 
'After the first two novels in the series, we have a finale that grips like a vice, and is full of the pace and all the imaginative and descriptive flair we have come to expect from this remarkable author.' Amazon
 
'The characters are believable; it is beautifully written, with page after page of powerful imagery; it is utterly compulsive and inventive reading for young teens.' Birmingham Post