From the Moscow suburbs into Asia and churning toward the icy Pacific, it's Grand Hotel on wheels--with one highly reluctant, highly important passenger: American leukemia expert Dr. Alex Cousins, whose reward for having gotten Soviet General Secretary Dimitrov into temporary remission is a trip home, the long way. But Alex might not even make it to Yokohama, since he knows (and is tempted to reveal) paranoid Dimitrov's secret deathbed plan--to take a few million unfriendly neighbors (""I will make Chinese stew"") along with him when he goes. Also on board: anti-Dimitrovian KGB agents (including Alex's compartment-mate, then bunk-mate, Tartarishly luscious Anna Petrovna from Irkutsk); Dimitrov's missile expert, General Grivetsky; a persecuted Jew and his frail, fearful non-Jewish wife, harboring illusions of a Siberian-Jewish enclave almost as welcoming as Israel; crippled Godorov, carrying out a 30-year-plan for vengeance at one of the Trans-Siberian's 80 stops; a breathtakingly bratty kid; and a half-dozen others--tourists, politicos, hired help--with stories of their own. The debt to Hitchcockian rail suspense is enormous--there's even a Lady Vanishes spinster entrusted with a secret--but industrious Adler (his third book in 18 months) recycles the train-leaps and corridor chases with unhysterical energy and drops in enough realski detail (steaming samovars, non-stop vodka, defunct menus, ""Yellow Rose of Texas"" muzak) and cagey sentimentality to keep the axles greased. Belabored sex and belabored debates on medico-political ethics aside, this Express stays on non-rusting, trusty tracks and makes enough of the right stops to accommodate travelers who aren't in a hurry.