Cape Cod on a mid-June morning is as rainy as all the East Coast has been the past few months, and since Paul Theroux recently arrived at his home there from his other home in Hawaii, he could justifiably be unhappy about the weather. “It’s been a wet and clammy spring,” he says. “But it’s okay. I’m a gardener, and when you plant things, you don’t want blazing sunshine in the beginning. My plants have already started to grow—it’s going to be a great summer, you’ll see.”

Such copacetic sentiments may seem out of character from a writer known for having a sharp tongue to match the sharp eye he has cast on his subjects in both fiction (The Mosquito Coast, My Secret History, and many more) and nonfiction (The Great Railway Bazaar, The Old Patagonian Express, and many more). Indeed, Theroux at age 78 voices his opinions as forcefully as ever. But he has a warmer side evident both in conversation and in his latest travel book, On the Plain of Snakes: A Mexican Journey, which Houghton Mifflin Harcourt will publish in October. Theroux profiles with compassion and respect a diverse group of migrants detained at the U.S. border and drives south into Oaxaca—home to many such migrants and one of the poorest states in Mexico—to find much more than poverty and desperation.

“The per capita income in Oaxaca is the same as in Kenya and Bangladesh,” Theroux says. “You’re dealing with people who have very little money and get very little help from the government. But they have a great culture they’re very proud of, their family values are very strong, and they’re very self-sufficient and creative. They mend their clothes; they fix their shoes; they’re actually able to take something that’s broken and repair it; they have a lot of cottage industries. I admire that, and I admire the ones who pick up and go to the border. Most of the people I’ve met who crossed the border just wanted to earn some money to send back and then go home; they weren’t here to go on welfare or be the parasites they’re identified as.”

In fact, Theroux says, “the book was inspired by everything that Donald Trump and other people were saying during the presidential campaign about Mexico, Mexicans, and the border—their uninformed opinions and stereotypes.” He adds, “One of the great reasons for traveling is to destroy stereotypes, to see people and things as they really are, to see the dynamics and the complexity of a country. As soon as he started saying things like, ‘There’s too many of them, they’re coming over the border, they’re rapists,’ I had a great reason for taking a year or two to get to the bottom of it.”

Though some of his most famous journeys have been by train, Theroux chose to explore Mexico in a car, as he had done for his previous book on the American South. “I felt liberated by driving, even though people told me not to,” he says. (Mexico is notorious for tourist carjackings.) “You see so much on a road trip; I felt that when I wrote Deep South as well. Some of the time in Mexico I was anxious: on a back road, or in the late afternoon when it was starting to get dark, or at a roadblock, or with a policeman.”

Theroux notes that he had several unpleasant encounters with corrupt cops who threatened to confiscate his car unless they were paid off. “The police are all sorts; I met some helpful ones, but some are very crooked, and some are indistinguishable from the cartels,” he says. “My car had Massachusetts license plates, and that marked me as a gringo. In travel, one of the most unhelpful things you can be is conspicuous; the greatest thing is to be anonymous.”

Nonetheless, Theroux stayed with his car. “Taking that risk and doing it my way was helpful,” he says. “You have a lot of mobility in a car that is unavailable to anyone waiting for a train or a bus. To write a book, you need a lot of mobility and a way of meeting people, and you can’t do it flying into a city and taking a taxi to the hotel. You need to see the edges of places, you need to cross borders, you need to be in the underserved places, the hinterland. Getting to Mexico City is very easy, and it’s a great city, but that’s not Mexico.”

Theroux did spend some time in Mexico City, teaching a 10-day workshop, and he writes warmly in On the Plain of Snakes about his students, who became friends. But he says he remains firmly convinced that “there’s a certain artificiality about Mexicans in Mexico City trying to figure out something to write about.” He adds, “The great lack in Mexican literature is that people don’t write about the rural areas—the regions and towns where life is hard and people are struggling but making do. People felt that magical realism answered their questions about how to penetrate the conflict in their country, but the style and subject matter of magical realism don’t answer anything. It’s a distortion of reality and an evasion of what life is really like. It seems to me a novelty that was picked up and promoted as a movement. As soon as something gets taught in a university, it’s over!”

Theroux goes on: “There are certainly great books that could be described as magical realism: Borges’s short stories have this sense of mystery and magic, García Márquez definitely, some others. But a movement starts when people pick up a style and begin imitating it, and I’ve always felt that style is something that comes from within you; it isn’t something you put on like a costume. When I was in college in the early ’60s, the writer was Ernest Hemingway, so writing like him—in short, declarative sentences—was supposed to be the way to go. Then it was ‘the wasteland’: Samuel Beckett, the end of the world, ‘It’s all going wrong.’ I’m not disparaging Hemingway or Beckett; they figured it out for themselves. The great writers should not be imitated; you need to figure out your style for yourself. Writing, in my opinion, should be a personal expression of what you see in the world, made powerful through imagination.”

Writing is also, in Theroux’s opinion, something one learns by doing. “The law that rules the arts is excess,” he says. “The more you write, the more you are able to write; the more you travel, the better you are able to travel. You have to keep doing it, and that’s where style comes from. One book doesn’t make you a writer; I’m much more on the side of Joyce Carol Oates and Georges Simenon, people who just keep at it all the time.”

Unsurprisingly, Theroux is already at work on his next book, a novel. “It’s set in Hawaii, and that’s all I can say about it,” he says. “But it’s keeping me busy. I’m much happier when I’m writing, rather than playing golf or being retired. Writers don’t retire; they can’t—it’s not a job. What would you retire from?”