His Dark Materials (Series 2)

Series 2 begins after Lord Asriel has opened a bridge to a new world, and, distraught over the death of her best friend, Lyra follows Asriel into the unknown. In a strange and mysterious abandoned city she meets Will, a boy from our world who is also running from a troubled past. Mrs. Coulter searches for Lyra, determined to bring her home by any means necessary.