Ghost Train to the Eastern Star, by Paul Theroux

Train travel, that glorious suspension of the self, has been Paul Theroux's prime signature as a non-fiction writer. Vagabond, lightly luggaged, "beneath notice" in comparison to plane or car traveller, the train passenger is freer than both yet still attached to the earth, able to let the passing landscape take the place of thought, the rails take all the decisions. Theroux knows exactly what Chekhov was talking about when, after the fiasco of the The Seagull's first night in St Petersburg in 1896, he left for Moscow on the first train – one that took 22 hours. "So much the better," the playwright told a friend. "I shall sleep, and dream of fame."

Because of trains, Theroux doesn't need to dream of fame. The Great Railway Bazaar, which in 1973 took him through Europe, the Middle East and Asia up to Japan and then back across Russia, made his name. Deciding to travel "in my own footsteps" 33 years later, his dreams are mostly of finding places unchanged, of reunions and revisited pleasure. The world is transformed, and the new book not a mirror of the old; he was refused a visa to Iran and decided, out of self-preservation, to avoid Pakistan and Afghanistan.

Nor is the 66-year-old Theroux a mirror of the young. On the night train to Tash-kent, surrounded by Uzbeks taking the train because they were poor, enjoying the fact that "the old world still existed", he writes that "here as elsewhere, I felt I was the fortunate traveller". His preoccupation with his own fortune is not just to do with privilege or liberty: behind it there seems to lie a peace-making with his earlier hyper-critical self. "Wisdom is a butterfly and not a gloomy bird of prey," he quotes Yeats. But in books such as The Old Patagonian Express or The Happy Isles of Oceania his wisdom was exactly that. Here it isn't – though it is a butterfly of massive mileage and pagination.

What does he find? Grotesquerie in many places he returns to: modernity and stealthy horror in the outsourcing explosion of Bangalore, oppressive hygiene in Singapore. Worse, in the new countries he visits: mendaciously modern Georgia, Azerbaijan and the "stans" of what was Soviet central Asia, whose bullied people, despite their leaders' boasts of progress, mostly want to emigrate to America.

He praises Istanbul "for its completeness"; Sri Lanka has "kept its soul" (because the Tamils have kept the tourists away). He meets engineers, businessmen, monks travelling lighter than himself; Jains, Sikhs, Buddhists; writers – Orhan Pamuk, Elif Shafak, Haruki Murakami, Pico Iyer, Prince Charles. Conversations become relationships (not with the Prince), and their pleasures and commonplaces are sometimes too scrupulously recorded.

Burma is the country he forms the strongest liking for, its preservation and people's kindness a sad result of dictatorship. At Mandalay, over several sunny days, he befriends an educated rickshaw driver his own age and finishes by giving him an envelope containing enough to retire on; at Pyin-Oo-Lwin he checks into Candacraig, the hotel whose manager he wrote affectionately about in The Great Railway Bazaar.

The old man is dead; his son invites Theroux home. "And so I sat there, and drank tea, and was happy. It was a homecoming I had not expected, like a visit to generous grateful relatives I had not seen in decades. Nothing like this had ever happened to me among my own family."

His account's one oddity is its unselectiveness, almost every kilometre recorded. It is not pacifying to be told on page 443 that "If you have got this far in this book" you are a "serious and omnivorous" reader. There are vestiges of the old Theroux philistinism too – muttering an oath at an Orthodox priest who shoos him away from an icon ("Up yours") – and mistakes: Graham Greene's companion Yvonne Cloetta never divorce her husband Jacques. Yet for his spartan love, as a traveller, for the aesthetic of trains and slowness, for his inquisitiveness and fluency, for his sympathy and sadness at the world's degradation and transformation, this ranks as one of his most human books. My final reaction was to have enjoyed it as a kind of wise commonplace book. Because wisdom there is in it; and this time, it seems he is happy for it not to be all his own.

Julian Evans's life of Norman Lewis, 'Semi-Invisible Man', is published by Cape