Gay Schaefer is a sultry truck dispatcher who is determined to ignore smalltown conventions and possess her life - to make it "original, graceful, adventurous." Separated from her husband of fifteen years, she meets him once a month at the Desert Oasis Motel for glorious carousing, but pretends they are divorced for the benefit of her teenaged daughter.

Meanwhile, hanging around with the local basketball coach sends a strange charge darting through her chest - a casual affair, at first, that threatens to upset the balance of her carefully constructed life.

Gay's daughter, Rita, is muddled, pudgy, obliged to admit that she, unlike her mother, doesn't "know how to dress for disaster." She doesn't even know whether it actually spells disaster when the river behind her house - the Rio Grande, chugging through New Mexico on its way to becoming the border - turns black, black as coal or oil or death, the night before she starts high school.

During the year beginning that night, disaster does seem to stalk Rita, getting more and more tangible, shaking even her mother's self-possession. It's got something to do with her best friend, Cecilia Calzado - and with Cecilia's brother Enrique, whom Rita starts dating, even though he's still in junior high - and with the fact that years ago Mr. Calzado had moved his family out of the shabby colonia across the river and earned the wrath of a menacing person named Rudy Salazar.