The Ruined City — John Wilson

Howard is a lonely, geeky tenth-grader dealing with a father who's had some kind of breakdown, a flaky, overprotective mother and frightening waking dreams. Then he meets Cate, a strange girl who convinces him that he is an Adept, which means he can communicate through dreams with other dimensions and, under certain circumstances, travel between them. Howard discovers that our world is only one of several dimensions swirling in time and space, and that one of the others, peopled by unimaginably powerful monsters, is approaching Earth for the first time in millennia. The last time the dimensions coincided, our world was saved by the breaking of a powerful golden mask in the Chinese city of Sanxingdui. Together, Howard and Cate travel through time and space, meeting other Adepts and avoiding lurking monsters, in a quest to find the three fragments of the golden mask and prevent it from falling into the wrong hands.