Sacrament of Night — Louise Cooper

They've been visiting the human world for centuries, the strange, frail, totally colorless denizens of the Twilight Dimension. Lured by the color, the brightness, the sheer vitality of mankind's world, they mean no harm--but few of them ever return home. Foss Agate, well-to-do physician and dabbler in the 'supernatural sciences', has a burning ambition: to break the secret of the gateway between the worlds by capturing a living twilight creature. But his captive is no ordinary twilight dweller, Charn in an emissary of his queen, sent on a mission to discover the fate of her son and heir, who vanished years ago within the human world. Torn by loyalty to Foss and compassion for his victim is his daughter, Calliope--a young girl who cannot help but fall prey to Charn's spell and who holds the key to a long-hidden secret. But before she can unlock the door to the past she must overcome the fear that threatens to destroy her. Fear of the unknown. Fear of the Sacrament of Night...