I'm coming round to the opinion that what happened to Schrenk in Lubyanka was not primarily because he was an agent. I think it was because he was a Jew and a dissident. That Quiller does not see this initially confirms the self-focus of his personality.
Unfortunately, state-sanctioned anti-Semitism has been a constant fixture under many regimes in both Old Russia and the Soviet Union. In TSS, we are repeatedly reminded of this feature of Russian life, through Schrenk's association with dissidents such as Natalya, through references to the Borodinski trial, and finally (most powerfully) through Schrenk's specification of the religion of the male figure ("Jewish husband") in the "toy" he describes during his showdown with Q in the apartment. My sense is that Hall, by dwelling on these elements, wishes readers to sympathize with Schrenk's goal of killing Brezhnev and perhaps others of his regime. Moreover, I don't think, as I have in times past, that Schrenk was a madman; rather, his motivation seems almost chillingly rational--to remove an ongoing threat to friends whose sympathies and cause he shares.
Another goal of TSS seems to be to comment on the variety among individuals with respect to how much they can take before lashing back at an oppressor. Eventually, what makes oppressive abuse "personal" to an individual is that the oppressor finally strikes a nerve over what is important to *that individual.* Given what motivates Quiller, finally, over the edge (personal insult), versus what motivates Schrenk (removal of the head of a violently repressive regime), I cannot help admiring Schrenk and being somewhat less admiring of Quiller.