Writing at the height of her powers, Alice Hoffman conjures three generations of a family haunted by love.     Cool, practical, and deliberate, John is dreamy Arlyn's polar opposite. Yet the two are drawn powerfully together even when it is clear they are bound to bring each other grief. Their difficult marriage leads them and their children to a house made of glass in theConnecticut  countryside, to the avenues of Manhattan , and to the blue waters of Long Island Sound. Glass breaks, love hurts, and families make their own rules. Ultimately, it falls to their grandson, Will, to solve the emotional puzzle of his family and of his own identity.