For two years Ashley Colton, a rough, ragged beauty in her mid-twenties, has walked a tightrope, trying to prove that she is fit to be a mother and regain custody of her son. She has survived on a series of minimum wage jobs and endured the probing scrutiny of home visits from Social Services. Cynical and embittered, she is convinced her son was taken because she is poor, and she carries a class rage that is difficult to control. But while Ashley sees herself as a victim, we see a woman who has lost her child because she is not ready to be a mother.

A surprise visit from her father, a truck driver living in Mexico, brings Ashley back into a turbulent and unresolved relationship. On a trip to Nuevo Laredo, she discovers that her father is smuggling immigrants across the border. Suddenly, in the vast, unforgiving landscape of south Texas, Ashley glimpses a solution to her problems and is lured by the prospect of easy money into the role of a coyote. Her improvised plan quickly goes awry, and Ashley finds herself stranded with a young girl whose mother disappeared in the late night river crossing. Failing in her attempts to abandon the girl, she begins a journey in search of the girl’s missing mother.

Together with the girl, Ashley travels through the borderlands of Nuevo Laredo and along the banks of the Rio Grande, retracing the steps of the immigrant journey. When she finally learns that the girl's mother drowned, Ashley decides to bring the girl back to her village in southern Mexico. Along the way, she discovers something unexpected, something she didn't even know she had - her own mothering instinct.