Ephemera, book 1: SebastianAnne Bishop2006

A world of shifting lands connected only by bridges, Ephemera has been kept stable by the magic of the Landscapers. In one land where night reigns and demons dwell, the half-incubus Sebastian revels in dark delights. But then in dreams she calls to him: a woman who wants only to be safe and loved-a woman he hungers for while knowing he may destroy her.

But a more devastating destiny awaits Sebastian, for in the quiet gardens of the Landscapers' school, evil is stirring. The nearly forgotten Eater of the World has escaped its prison-and Sebastian's realm may be the first to fall.