Behind the Smith pseudonym is Joyce Carol Oates, who's in a playful, slightly nasty mood here--taking a glossy, shallow heroine (intentionally unsympathetic) through some creepy, modern psychosexual variations on a familiar gothic, romance scenario. Molly Marks--""a very pretty young woman who suspects at times she is a little too clever for her own good""--should be blissfully content. She has a cushy PR job, good looks, a quick (if superficial) mind--and has just moved into a sleek Connecticut apartment with her new lover, psychotherapist Jonathan McEwan: serious, workaholic, gentle, loving, and ready, perhaps, for marriage. But Jonathan has one sore spot, one thing he won't talk about: a deep hatred for long-estranged brother James, his identical twin, who was responsible for some mysterious, bygone tragedy. Like Pandora, of course, Molly can't bear not knowing all the juicy hidden details. So she secretly seeks out brother James, an N.Y.C. shrink who is Jonathan's psychic opposite: cold, sadistic, hedonistic, very much the ""dominant"" twin. Molly poses as a patient; James heaps abuse on her, then seduces her, secretly knowing about the Molly/ Jonathan relationship. Worse yet, after Molly gets pregnant (by which twin?), Jonathan uncovers her deception and recoils. (""I love you but I can't trust you."") Meanwhile, James--intent on keeping their kinky affair going--harasses Molly with tricks, come-ons, escalating threats. And finally, after learning the not-very-surprising Truth about the twins' tragic past (a fatal triangle involving Jonathan's high-school sweetheart), Molly ends up in a Lady-or-Tiger tableau/showdown with both twins, good and evil, unable to tell them apart. This ending is a fizzle, the appropriate windup to a plot that seems arbitrary throughout, whimsically contrived by the coolly detached narrator. But if too blatantly artificial to generate involvement or chills, Oates' ironic, slick potboiler--with echoes of everything from Lohengrin to Rebecca--is icily diverting most of the way through, faintly preachy underneath, and far more readable than much of the author's more ambitious recent fiction.