This novel is about the perplexing problems of justice. By showing a whole cast of characters whose allegiances are questionable (because they're literally spies), a tense tone is set that carries through the novel. One by one, spies come to their fateful death, as the moral fabric of their allegiances fade into the background. In the end, the spies become independent to an extent, motivated by success or failure in a personal sense, so much so that the good guys are willing to partner with actual Nazis instead of risking failure.
Another possible reading comes from reducing each character's motivation to their psychological obsessions and extreme allegiances. It would be easy to question the humanity of an agent like this, so this reading has more of a thematic, moralistic angle. Of course all interpretation is speculative, but actually, the most sufficient explanation seems to be somewhere in the middle of these two theories.
In other words, the book is an exposé of moral decay as the motivations of the individual become more extreme, which looks like allegiance to the high-stakes conflicts of the Cold War, but in reality is just regular human competition and fear of death.
In other words, no matter how deeply the reader travels into high espionage, the spies in question have survival and competitive victory on their minds, just like any war anywhere on the earth. This is the effect of the novel, that through the espionage, an entire proxy war is fought.
