Crown of Earth's Desire by Terry Ho

An American student, Keith Anderson, comes to Singapore to complete his college thesis and rediscover his Straits Chinese heritage. Instead, he and three Singaporean friends are swept into an enchanted world of spice harbours and tropical rainforests. They are caught up in a quest to save the Kingdom of Turasik, which is embroiled in political turmoil under the shadow of a foreign enemy. To return with his friends to their own world, Keith must first journey across haunted jungles to seek answers from the Oracle of Xua. Danger lies in wait at every turn – from armed bandits, assassins, guardian spirits and malevolent sorcerers. At the heart of the quest is the mystery of the Forbidden Hill, a seat of enormous power once ruled by the enigmatic god-king, the Raja Shulan. All is not as it seems, as the Spirit of the Raja is invoked in ancient rites on the Forbidden Hill – for what is at stake is not just the Kingdom of Turasik, but the fate of the two worlds, and the universe itself.