The Line Becomes a River: Dispatches from the Border by Francisco Cantú is a work of literary nonfiction published in 2018. It was a New York Times best-seller, a finalist for the National Book Critics Circle Nonfiction Award, winner of the Los Angeles Times Book Prize in Current Interest, and was named a Top 10 Book of 2018 by NPR and The Washington Post. The book combines memoir with history, anthropology, sociology, and psychology to paint a full portrait of what the US-Mexico border means as a place and a concept. Cantú served as a US Border Patrol agent in Texas, Arizona, and New Mexico from 2008 to 2012, working in the field and in intelligence offices. He has been the recipient of a Fulbright fellowship, a Pushcart Prize, and the 2017 Whiting Award.

Francisco Cantú is a third-generation Mexican American immigrant raised in Arizona by his mother, who served as a park ranger in the desert. The physical and emotional terrain of the border is something he wishes to understand on a human level, which leads him to join the US Border Patrol, despite his mother’s concerns that the institution will corrupt his ideals. The book is split into three parts, chronicling Cantú’s time working as a Border Patrol agent in the field, in an intelligence office, and after his resignation from the force, when he returns to civilian life and graduates school. His personal narrative is told primarily in short vignettes that are braided together with historical and journalistic research, cultural sociology and psychology, Mexican literary references, descriptions of dreams, conversations with Cantú’s mother, and more, to create a complete picture of the way the US-Mexico border has embedded itself—as a place, as an ideal, and as a set of ethics—in Cantú’s mind.

Part 1 follows Cantú’s time as a field agent, chronicling his various encounters with undocumented migrants and his fellow Border Patrol agents, many of whom are Latinx or originally from Mexico themselves. Despite his college degree in international relations, he wishes to gain hands-on experience relating to border policy and the ways migrants are treated. As he adjusts to life in the Border Patrol, he arrests undocumented migrants and witnesses firsthand the horrific conditions the migrants endure for the chance to cross the border into the United States. These migrants are more than likely deported back to the often dangerous and violent places from which they came. Though he can offer them water or snacks, Cantú realizes there is little he can do to help them in a meaningful way. He begins having stress dreams about his time on the force and grows increasingly paranoid even while not on the job. These experiences are accompanied by a history of the US-Mexico border, primarily from the 19th century to the ongoing Mexican war against drug cartels and the widespread violence that has ensued. The American desire for a physical border, as denoted by “monuments” placed by surveyors in the 1800s, becomes increasingly difficult to negotiate over time, given the harsh and destructive desert conditions.

Cantú is transferred out of field work to a Border Patrol intelligence office in Tucson, Arizona. His new job means surveilling camera and photo footage from the desert and conducting intensive research into drug cartels’ activity and smuggling. While this job is far safer than his old position out in the field, Cantú is continually exposed to graphic photos and videos of violence and mutilated bodies exposed to the elements. He intersperses Part 2 with research he has done about trauma and violence along the border, especially related to the drug cartels. This includes interpretations of corpse mutilation, a timeline of femicide in places like Ciudad Juárez, the role of pain in Mexican literature, documentaries about sicarios (Mexican drug cartel assassins), and more, building a growing sense of pressure, fear, and tension. His nightmares worsen, and a dentist notices that he is grinding his teeth. Even after a transfer to the El Paso Border Patrol office, where Cantú befriends fellow officers Beto and Manuel, Cantú realizes he is not cut out to be a Border Patrol agent. He receives a fellowship to study and research abroad, and resigns from his position.

Part 3 jumps to Cantú more than a year later, living as a civilian and attending graduate school for writing while working as a barista. He befriends a maintenance man named José, and their friendship grows over two years. But when José doesn’t show up for work for three weeks, Cantú discovers the truth: José was undocumented. He crossed the border to see his dying mother but was arrested by Border Patrol as he tried to sneak back into the country. Desperate to redeem himself for his past actions as a Border Patrol agent, Cantú reaches out to José’s wife Lupe to offer assistance as a translator and friend. He grows close to the family as he helps them navigate the obfuscating and complicated immigration legal proceedings, taking José’s children to see their father in detention centers and ferrying paperwork to their lawyer. Cantú finally sees the other side of his job as a Border Patrol agent, and the often terrifying consequences for the people he arrested along the border. José is eventually deported with little warning, but Lupe tells Cantú he will keep trying to cross until he makes it. Struggling to make sense of his own emotions, Cantú finally confides in his mother the pain and confusion he feels, and she affirms his grief, offering an interpretation of his years of nightmares and recommending that perhaps it was time for him to listen to José’s side of the story. The final chapter shares José’s perspective on the other side of the border, making clear that he promised to reunite with his family, and he will stop at nothing to successfully make it back to them in the United States.

In an Epilogue Cantú has a dreamy, peaceful encounter with a Mexican villager while hiking along the border in Texas. The man brings him to his village across the border for breakfast. The book ends with Cantú swimming in the Rio Grande, a river that separates the two countries. As he swims from one side to the other, he forgets which side belongs to which country, and the borderline becomes blurred.