COMBINE FOR A MOMENT the descriptive power of a James Salter novel (oh, those beautiful things!) with the dialogue of a John Fowles novel (Daniel Martin). This is the feeling one gets reading Michael Cunningham's latest. By Nightfall, like The Hours, is chock full of literary reference, especially Thomas Mann (Death in Venice), not Virginia Woolf. Peter, gallery owner living in Soho, has worked the New York art scene for decades. His wife Rebecca is increasingly estranged, and his grown daughter Bea is also polite, but absent. He moves through Soho, taking night walks and, by day, making deals like a sleepwalker, until Rebecca's troubled younger brother, Mizzy, comes for a visit. Mizzy is an addict, a beautiful addict. He reminds Peter of one of those medieval knights lying, arms crossed over chest, in stone at the Cloisters. Peter falls in love with him, in a dangerous version of a midlife crisis. He and Rebecca have lived "a gorgeous imitation of the regular," and Peter is tired of it. He has enforced his aesthetic on his daughter, who never felt good enough, and sacrificed real love for something trendier. Now, he is paying the price.