The part I remember most about the book is a scene where the three friends are walking across a huge desert to reach a fortified city with high copper walls that bake in the sun. The desert is very dangerous because there are giant sand creatures who live in pits in the sand. The girl falls into one of these pits and it ends up being a burning tunnel of some sort which both other boys follow her into.
Perhaps there is another scene about him gazing into a small pond or fountain of clear water like a mirror to see his "gifts" or "future" or some sort of power. Not sure though.
Thank you for you help!