Sceptre of Sea and Sky by Terry Ho

Returning to the enchanted world of Erda in search of their missing friend, Keith, Anna and Vijay are once again enlisted in the desperate struggle against the Dark. Keith sets off for Chapterhouse Manaung, where he is to receive training in the arts of the magi. Anna and Vijay, accompanied by the Royal Mage of Turasik, a warrior woman and a runaway boy, embark on a voyage of a thousand leagues that will take them to the dominions of a lustful queen, a city under the sway of a sinister abbot, and a land of vengeful spirits. In a garden of dreams and nightmares, their destination is revealed: the Place Where Sea Meets Sky, where on of them must make the ultimate sacrifice. There is little time. In the icy North, the iron fetters of the Frost Giants are loosed, unleashing primeval powers not seen on Erda in millennia. And beyond the dusky skies, an ancient evil looms at the portals of Space and Time.