Some novels you nibble away at, half unthinking. Anne Enright's prose bites back. The Irish author of The Portable Virgin and The Wig My Father Wore has produced a third book as unexpected and lively as a miracle child--or is it twins? She tells the story of a Dubliner whose mother died in childbirth. Maria is now 20, living in New York, cleaning houses, taking drugs, sleeping with strangers, and generally being in a funk. In a lover's bag, she finds an old photo of a girl who looks just exactly like herself, dressed in clothes she's never owned, posing with people she's never met. But this isn't some gooey, alternate-reality identity fantasy. Maria has, in fact, a twin sister. Though each is unknown to the other, we learn both their lives inside out as they head toward a giddily inevitable meeting. This twinning tale suits Enright's style right down to the ground: Her mandate is to bump us into awareness, and if it takes double heroines, so be it. Her language does the rest of the work. On the very first page, for instance, she freshens the simple act of holding a baby into a joke: "And they handed her on from arm to arm, with the dip that people make when they give away a baby--letting her body go and guiding her head, as though it might not be attached. Nothing worse than being left holding the baby, they seemed to say, except being left with the baby's head." In fact, Enright is transfixed by the weirdness of the body, as when Maria