Six Moon Dance by Sheri S. Tepper

It was many years ago that humans came and settled the world of Newholme-cruelly bending the planet to their will; setting down roots and raising up cities and farms and a grand temple to their goddess.But now the ground itself is shaking with ever-increasing violence. And the Great Questioner, official arbiter of the Council of Worlds, has come to this isolated orb to investigate rumors of a terrible secret that lies buried deep within Newholme's past—a past that is not dead, not completely. And it will fall to Mouche, a beautiful youth of uncommon cleverness and spirit, to save his imperiled home by dicovering and embracing that which makes him unique among humans. For every living thing on newholme is doomed, unless Mouche can appease something dark and terrible that is coiled within...and surrender to the mysterious ecstatic revelry taht results when the six moons join.