During dinner aboard the train, there's another telltale sign that "Nash" wasn't who he seemed to be. When Grant "accidentally" spills Tania's wine glass, then fills it again and slips in some pills, look at how he's pouring the wine: he's holding the bottle by the neck rather than the body◊, a big mistake among wine connoisseurs like Bond.
In the book, Bond refers to Guy Burgess and Donald Maclean, two diplomats with links to British intelligence who were actually Russian moles, both of whom had defected to the Soviet Union in 1951. Fleming wrote this in March 1956, less than a month after their their presence in Moscow had been made public knowledge. Bond goes on to point out that of the two, Burgess would be more likely to make contact with a British agent from his own social group stationed somewhere behind the Iron Curtain, giving rise to the prospect of turning him into a double agent — and in Real Life, Maclean assimilated into life in Moscow much better than Burgess did. A couple of chapters earlier, Klebb mentions that Grant will be trained in how to act like an English gentleman by a defector who used to work for the Foreign Office; although not named, this person could be either Burgess or Maclean (more likely the latter).
Tatiana, a loyal Soviet clerk that's good at her job and has no malice against anyone, is manipulated by a traitor through her devotion to country to commit treason and played by Bond to defect out of infatuation as the audience fully knows Bond has no intention of settling down with her, likely leaving her to an uncertain future in an enemy country.
◊, a big mistake among wine connoisseurs like Bond.
