The Wizards of Once by Cressida Cowell

Wizard boy, Xar, should have come into his magic by now, but he hasn’t, so he wants to find a witch and steal its magic for himself. But if he’s got any chance of finding one, he will have to travel into the forbidden Badwoods. Xar doesn’t realise he is about to capture an entirely different kind of enemy. A Warrior girl called Wish. And inside this book, at this very moment, two worlds collide and the fate of the land is changed forever. Xar and Wish must visit the dungeons at Warrior fort, and face the evil Queen. But something that has been sleeping for hundreds of years is stirring …