The Truth-sayer — Sally Prue

Nian is 'discovered' as a boy with special powers, and whisked away to be an apprentice in the House of Truth. He immediately resolves to escape - but there's only one way he can think of to get out, and that's to learn to fly. Unfortunately his powers are rather hard to control, and the
process involves a certain amount of banging his head on the ceiling...

Then he finds a place where the boundaries between the worlds are thin, and he stumbles into our world. There he meets Jacob, who helps him as he learns to speak the language and to start to come to grips with the funny habits of people in this world, and to start to see how he might find a place
here. But then the House of Truth send someone through to hunt him down and fetch him back, and the equilibrium of the worlds starts to break down.

Nian knows he will have to go back - but first he will have to rescue his pursuer, who is causing mayhem wherever he goes, and on the way help Jacob and his family through some tricky situations. On his return to the House of Truth he will use his new experiences and knowledge to change the way of
life there forever.