White Plains, by Rebecca Perkin
'Power Can Come To Anyone.'
Ever since Samuel's twin brother died almost a year ago, Samuel has wanted to escape reality. But when he falls through an open gateway into another world, a world at war, there's nothing he wants more than to get back home. Discovering that gateways are forbidden, Samuel has no choice but to go on a journey with plain seeker, Alexis. Together, they must deliver a sacred artefact to an enchanter if Samuel is ever to find his way back to Earth. Their voyage will take Samuel across a whole new world and bring him more power than he ever thought possible.