TSS is a strange novel, by turns a morality tale, a grim portrait of espionage in the old Soviet Union, and oddly, a curiously naive estimate of what, realistically, might be expected to have occurred in such a hostile environment.
TSS has one of my very favorite beginning sequences in all the Q-orpus. As Penny's so perceptively pointed out, at the beginning we get a vivid description by, and of, Q engaged in recreational activity while on leave. Then there's the conflict between Q and Croder, the later meeting at Tempelhof, and the revelation of the incredible blunder (about which more later) in which a superstar like Shapiro, with a headful of damaging information, gets seconded to the field executive pool. The passage into the USSR is wonderfully done (a damn' sight more believable than the Finback episode), and the briefing by Bracken in the car one of the finest Q/DiF moments in the Q-orpus.
The good news about the novel is that these opening sequences are both believable and realistic (with nice little touches like Dr. Steinberg kicking Q out of his office when he asks too many probing questions about Shapiro). The operation is perfectly plausible, if you suspend disbelief for a moment about the likelihood of Shapiro's having been seconded to the field exec pool.
The bad news is that once in Moscow, the plot becomes progressively more unbelievable, to my mind beginning its decline with Q's escape from the van on his way to the Serbsky Institute. I've never bought the idea that Vader's men would have let Q that close to the good Colonel after Q's having tried already to attack him by noticeably expert means (particularly when they think Q might know Schrenk, who'd already escaped from Lubyanka [not a van, but the *prison* itself]). Moreover, I think it unrealistic to suppose that Croder arrived in Moscow to "hit" Shapiro should the need arise, and I don't like the implied judgment that Croder's got to clean up Bracken's op; the failure's not Bracken's, it's Q's, and by default, Croder's for having roped Q, with his known romantic tendencies, into the mission. Finally, the idea that the Bureau could obtain such detailed intelligence about the limo contrasts sharply, jarringly, with the climate in the early part of the novel, where Q has to shadow-dance with untrained cutouts and get briefed with the KGB on his tail.