One idea or theme driving the narrative in TSS is pride and how it goes before a fall.  Of course, by this, the ninth Q-orpus novel, readers are pretty much resigned to Q's overweening pride.  But there's a lot of other pride propelling the Scorpion mission.  Just a few instances of pride and what it can cause you to lose:

1.  Vader's pride probably leads to his death.  Not only does he insult Q by saying what he shouldn't (that Q smells) but then he seems to feel obligated to rub it in by personally accompanying him to the Serbsky Institute.  Though we can't be sure of the normal procedure for transferring prisoners, I doubt it usually involved someone of Vader's rank; more likely, Vader's accompanying Q is an extension of his earlier pose of "brushing off a fly" after Q tries to attack him.  It seems likely Vader was saying to Q, "you just aren't lethal enough to shackle and send guards with," always a dangerous conceit to indulge in with Our Fave Ferret.

2.  Schrenk's pride loses him an old friend and gains him some dangerous new ones.  Under Croder's questioning, Q says Schrenk has a "degree of megalomania" [17:89].  The dictionary defines "megalomania" as "a delusional mental disorder that is marked by infantile feelings of personal omnipotence and grandeur."  Schrenk's belief that a bomb is the "only thing those bastards will listen to" is indeed the product of mental disorder; as the icy-minded Croder points out, to kill Brezhnev would bring unimaginable global geopolitical consequences, something an agent of Schrenk's experience ought to have known.  However, Schrenk's belief in his personal omnipotence means he can justify to himself even the horrifying action of exposing Quiller to the police and then daring to claim that it was okay, because Q knew how to "look after" himself (!) [14:62].  This is an incredible rationalization, given what they'd done to Schrenk in Lubyanka, and is testament to the self-focus of Schrenk's pride.  There's no concern for others in Schrenk's action:  it is pure self-indulgent vengeance, and the welfare of two countries, the rest of the world, and even the lives of trusted comrades in arms be damned.
3.  Croder's pride nearly loses the Bureau's best agent.  My theory (laid out in fragments in previous "Thoughts") is that Croder and at least some others knew all along that the real threat Shapiro posed had nothing to do with the Leningrad cell, but with something else he was planning.  Thus, Croder's offering Quiller that reason may have been a form of manipulation, designed to capitalize on the fact that Q'd previously worked with Schrenk and two other members of the Leningrad cell (Comstock and Whitman) [4:83].  Croder's overweening pride lies in his assumption that he knows Q so well that he can "be inside his head" (cf. Croder ordering Fane's bomb-planting in Q/N) and furthermore can control all the elements of the mission.  But he's well out of his depth here:  any of a number of things could've gone wrong in Schrenk's apartment, or outside it, and then the link to Schrenk would've been lost, either for the purpose of getting him clear or killing him.  I think it significant that Croder has to go to Moscow himself to clean up the mess that's happened on account of his too-prideful belief that only he can successfully take on missions that "others wouldn't touch."