Silver Light: Book 1 of Mothertree

Walde has inherited a forbidden power from his father, enabling him to commune with Thara, an enigmatic being that lives deep in the earth. Walde thinks he can keep this power a secret, but one day he slips. His father is blamed and executed, the body placed on a raft and sent down a rushing river. Walde breaks free and goes after him...only to discover that the execution was staged. Very much alive, his father floats off to a mysterious end. During Walde's perilous journey to rescue him, he learns what is truly at stake: not only his father, but also his people's entire way of life.