Paul Theroux has been called “The world’s most perceptive travel writer.” He’s spent over 50 years canvassing the globe and is the highly acclaimed author of such books as “Riding the Iron Rooster,” “The Old Patagonian Express: By Train through the Americas,” and – one of my favorite books of all time – “The Great Railway Bazaar.” He’s a novelist, too (“The Mosquito Coast,” “Saint Jack,”), but his latest continues with his wanderlust and explores a country close to home and immersed in immigration news headlines: Mexico. In “On the Plain of Snakes: A Mexican Journey” (Houghton Mifflin Harcourt), Theroux drives the U.S.-Mexican border, reporting his encounters with border-crossers, Border Patrol officers and humanitarian aid workers. He continues on to Mexico City, where he’s accosted by policemen wanting bribes, but makes meaningful friendships through a writing class he teaches. From the capital he goes into Chiapas and Oaxaca, where he meets with the iconic Subcomandante Marcos, rebel leader of the “Zapatistas,” who are sworn to defend Mexico’s indigenous people. The book is brimming with adventures, history, discussions on Mexican literature and splendid descriptions. Running all through it, however, is a profound humanity and reverence for the ordinary Mexicans who are Theroux’s main subject.

Theroux starts his journey because he is melancholy and restless, feeling old (he’s 78) “no longer interesting, parasitical, invisible to the young.” His remedy is this road trip, and the details of his travels in “On the Plain of Snakes” (the title is a translation of an indigenous place name) couldn’t be more crucial, informed, probing or kind.

As Theroux did in the eye-opening “Deep South: Four Seasons on Back Roads,” he drives his own car – and old Buick – across the 1,954 miles of the border. The drug-cartel violence ruining northern Mexico is highlighted, along with power abuses by the police and military throughout the entire country. Theroux learns of a cartel-related murder of 43 students from a teacher’s college, and is shaken down himself several times by shady cops. However, the common fear of these threats, Theroux observes, has “unified good people and created watchful communities.” Whenever he can, he talks to members of those communities, asking if they’ve been to the U.S. and, if so, what their experiences were.

No story is alike, but patterns surface. NAFTA’S introduction of American agri-business to Mexico, Theroux learns, has made it almost impossible for small farmers to live off their land. Instead they are forced into low-wage factory jobs on the border or illegal agricultural labor in the U.S. itself. He also discovers via the Los Angeles Times that a large number of economic migrants from India, Bangladesh, China, and even the Middle East have made their way lately to the U.S. via Mexico – something that hasn’t much registered in the news here, rightly overshadowed as it is by what Theroux criticizes as our country’s “barbaric and inhumane violence” toward refugees from violence in El Salvador, Honduras, and Guatemala, including family separations and child imprisonment.

Theroux thoroughly investigates migrant-labor policies, noting that one program in effect from 1942-1964 was ended over worries that Mexicans were being “exploited and manipulated as low-wage workers” rather than worries that they were stealing jobs from Americans. He has a keen eye for the tight bonds between cross-border communities. “Among other things,” he says, “the borderland is a living repository of native peoples.”

Originally the author planned on examining just the border, which he finds “a front line that sometimes seems at war, at other times an endless game of cat-and-mouse.” A consummate storyteller, he hears tales from dozens of detained migrants – teenage Daneris, escaping gang wars in Honduras; middle-aged Norma from Oaxaca, torn between family members on both sides of the border; Ernesto, a 70-year-old house painter facing a lonely future without his four estranged adult children. He observes Maria, a mother of three, quietly praying before a meal at a Nogales shelter, and writes “Sometimes a whispered word, or a single image or glimpse of humanity can be a powerful motivation for looking deeper into the world.”

And Theroux does go deep. He takes readers through the shaky and often brutal states of Oaxaca and Chiapas. He does not sanitize the trauma of poverty in Oaxaca, where per capita income is similar to Bangladesh or Kenya, nor does he minimize the dangers faced by migrants from Mexico and Central America hoping to enter the U.S. “On their trips through Mexico …migrants are brutalized, abducted or forced to work on Mexican farms, as virtual slaves,” he writes. “In the past decade, 120,000 migrants have disappeared en route, murdered or dead and lost, succumbing to thirst or starvation.”

Because he has his own transportation, he’s able to look beyond tourist sites to the turbulent, sprawling side of urban Mexico most visitors don’t see. The first big city he meets, Monterrey, an hour or so south of the US border, is “surprising for its obvious wealth, its boomtown bustle, and its intensive building.” Its educational institutions, high-tech companies and manufacturing facilities, he notes, leave the Texas towns on the border looking “sad” and “struggling” by comparison “another reason Mexicans feel belittled and misunderstood” by their neighbors to the north, Theroux suggests.

In Chiapas, where Theroux meets with the Zapatista rebels, and their masked leader, he experiences “a clarification of much that I had seen in my traveling life, an elaboration of the challenges of poverty and development, the curse of bad government and predatory corporations, the struggle of people living on the plain of snakes who wish to choose their own destiny.”

In the countryside, the author’s descriptions of his physical surroundings are impressive. “Black clouds were mounting ahead,” he writes on the road to Oaxaca, “building beyond the ridge, as dark as smoke billowing from an oil fire, thunderheads, tall and dense, closing in as they heaped up against the hills, as black as clouds could be, and really not like clouds at all but a black bulging wall about to burst.” But, he writes, “travel is less about landscapes than about people – not power brokers but pedestrians, in the long march of Everyman.”

Perceptive commentaries on Mexican art, literature and indigenous cultures (including a Zapotec “third sex” cross-dressing tradition in the southern city of Juchiteco) round out the book. Observing Day of the Dead festivities, Theroux turns to the late Mexican Nobel laureate Octavio Paz (“the most acute of Mexican writers on Mexican life”) for insight into what he’s seeing. “The Mexican,” Paz writes, “is familiar with death, jokes about it, caresses it, sleeps with it, celebrates it; it is one of his favorite toys and his most steadfast love…True, there is perhaps as much fear in his attitude as that of others, but at least death is not hidden away: he looks at it face to face, with impatience, disdain or irony.” That attitude rubs off on Theroux, leaving him “eager to wake each morning and see what the day would bring – even when what it might bring was a nighttime vigil in a cemetery and an array of skulls.”

Whether you’re a longtime Theroux fan like me or just curious about the Mexico beyond the headlines, “On the Plain of Snakes” is immensely gratifying. It’s obvious that Theroux wrote the book because he wants people to know that Mexico is not just “tacos, sombreros, and mariachis, it’s a big, complicated, interesting place. A big, vibrant country full of subtlety, cultural differences and a place that’s humane – it’s not a cartel-dominated place. The humanity of Mexico is what I’d like to see [readers] take away from the book.”