For Francisco Cantú, the border is in the blood: his mother, a park ranger and daughter of a Mexican immigrant, raised him in the scrublands of the Southwest. Haunted by the landscape of his youth, Cantú joins the Border Patrol. He and his partners are posted to remote regions crisscrossed by drug routes and smuggling corridors, where they learn to track other humans under blistering sun and through frigid nights. They haul in the dead and deliver to detention those they find alive. Plagued by nightmares, he abandons the Patrol for civilian life. But when an immigrant friend travels to Mexico to visit his dying mother and does not return, Cantú discovers that the border has migrated with him, and now he must know the whole story.