Half a lifetime ago, Paul Theroux virtually invented the modern travel narrative by recounting his grand tour by train through Asia. In the three decades since, the world he recorded in that book has undergone phenomenal change. The Soviet Union has collapsed and China has risen; India booms while Burma smothers under dictatorship; Vietnam flourishes in the aftermath of the havoc America was unleashing on it the last time he passed through. In "Ghost Train to the Eastern Star, "Theroux re-creates that earlier journey. His odyssey takes him from eastern Europe, still hung-over from communism, through tense but thriving Turkey into the Caucasus, where Georgia limps back toward feudalism while its neighbor