What becomes of the brokenhearted? Well, that sometimes depends on who does the heart breaking. In the case of Martha Horgan, the woman of Mary McGarry Morris' novel, The Dangerous Woman, heartbreak was at first a family affair, but by childhood's end it had become a community project. Born in the ''Other America'' of New England's back roads, Martha was raised by her father, a handyman with a knack for everything except fathoming his daughter's emotional waters. When Martha is made the victim of a grotesque sexual encounter in high school, the town excuses the behavior of its native sons by exaggerating her nuttiness. After that, well, that's really where the novel begins its close-grained observation of the way good citizens turn an emotionally disoriented girl into a social menace.
Morris, whose splendid first novel, Vanished, combed through the untidy mind of a teenage kidnapper, knows how to keep a balance between the wobbly inner lives of her outsiders and the external forces that finally drive them over the edge. A Dangerous Woman is all the more disquieting for its accurate portrait of middle-class anxiety about the mentally aberrant. B