Lightly mixing personal and family experience with an idiosyncratic social history of Irish immigration, Mathieus first book draws on her travels to Ireland and her interviews with the Irish in rural Roscrea and environs and in New York City to survey the landscape of emigration in Ireland and in the US. The author arrived in the small town of Roscrea, County Tipperary, in central Ireland, the year after she finished college, hoping to ``discover who stays in these unreconciled parts of the world, and ultimately who leaves them.'' She was interested in the question for personal reasons, her grandmother Sarah Reilly having emigrated from Ireland in 1912; spending six years in New York City, she married and moved west, eventually returning to Ireland in her 70s. Examining photographs of her great-grandparents Richard and Mary Reilly, described as the two who have ``presided over my life like childhood crimes,'' the author attempts to imagine their lives, looking for an explanation of why their daughter Sarah became an exile. As Mathieu began to conclude, migration is a ``complicated business.'' In New York she found the Irish she tried to interview were often suspicious and uncooperative. Many returned to Ireland, though the New York Irish continued to find unity in one another. Her detailings of light and skies, the changing patterns of the rural Irish cloudscape, and a particular ``scotch-colored'' Greenwich Village dusk suggesting perhaps that human seasons mirror the weather, Mathieu's nonscientific study is content to make few hard conclusions. Mathieu's title, from a word for the Irish that has also been used for American immigrants heading west by rail, has a strangeness and mysteriousness that Mathieu finds appropriate for her subject, its twists and turns, the shadowy nature of the immigrant experience.