Someone once asked Paul Theroux "What do you write about?" "Everything I see," answered the prolific Theroux, who, if you're counting, has written 14 travel books, 27 fictional works and one book of criticism. The answer itself was vintage Theroux: sly, smart and strident. The same can be said of the engaging and brilliant "Ghost Train to the Eastern Star," which can only add to his stature as one of our most agile and original writers.

The trip from London to Vladivostok seeks to retrace the author's first such journey recounted in "The Great Railway Bazaar," published 33 years ago when the younger Theroux was less accomplished, a worried man on the brink of divorce. It launched his career in travel writing; when shelves are clogged with punchless tips from Rick Steves clones, it's fair to say it's a genre in which he has no equal.

This more seasoned Theroux, remarried and confident, is now in his 60s, splitting his time between Hawaii and Cape Cod. To his credit he knows the dangers of the rerun, the devolution into gaseous nostalgia and narcoleptic fogeyism. He embraces his age; in fact he celebrates its realities:

"A great satisfaction of growing old -- one of many -- is assuming the role of witness to the wobbling of the world and seeing irreversible changes. The downside, besides listening to the delusions of the young, is hearing the same hackneyed opinions over and over ... the discoveries that are not new, the proposed solutions that will solve nothing."

This idea of aging with an attitude is a delicious, Therouvian subtheme throughout the book. Equally apparent is that the book can hardly help but reflect geopolitical changes since "The Great Railway Bazaar." Theroux looks out from his train compartment on a planet that no longer includes the USSR, a Vietnam under siege or an Indian economy stuck in the tribal past. It's a post 9/11 world, yet security is no more invasive than our own TSA once-over, or sometimes downright lax. He's not allowed into Iran this time and wisely chooses to forgo Afghanistan.

Theroux's quick assessments of national character might offend some, but veteran readers will find the author true to his rather dim view of human motives. Turkmenistan and Uzbekistan are mostly desperate countries that resemble the "humorlessness and paranoia of a police state." Cambodia is a "death-haunted country." Vietnam is cheerful, its economy booming, its people showing no signs of resentment toward the United States, even though we tried to obliterate it with "seven million tons of bombs."

As he often does, Theroux saves his worst venom for missionaries. In the Buddhist nation of Thailand he meets a Christian, whom he describes as "an oversized mongrel worrying a bone."

Her piousness finally gets the best of him, as he asks, "What is it with you people?" He is kinder to the Mormons trolling the mean streets of Vladivostok.

In almost every country, women old and young proposition him. Many are desperate to find a way to the United States. Others are in thrall to the darker edge of the oldest profession: sexual slavery. In the most haunting scene in the book, Theroux is exploring the seamier areas of Singapore. Approached by a pimp, he poses as a john, and finds himself in a warren of tin-roofed buildings housing Thai girls apparently held hostage. Some are as young as 14.

"One thin-necked unsmiling girl, with pale skin and a fragile body, narrow shoulders and no breasts, tried shyly, turning sideways, to catch my eye ... Was I imagining that she was twisting a little stuffed toy in her hand?"

Such heartbreaking encounters with people, and with a planet whose rising population leaves it more fouled by the minute, lead Theroux to a grim summary. "Most people on earth are poor. Most places are blighted and nothing will stop the blight getting worse. ... There are too many people, a great number of them spend their hungry days thinking about America. The world is deteriorating and shrinking to a ball of bungled desolation. Only the old can really see how badly the world is aging and all that we've lost."

These are not passing postcard dispatches or the low grumblings of a grumpy old man. They are the mature, hard-won conclusions of a writer who, though he does not suffer fools gladly, treasures the vanishing beauty and diversity of this beleaguered planet.

Stephen J. Lyons, author of "Landscape of the Heart" and "A View From the Inland Northwest," lives in Monticello, Ill.