The Spy Who Came in from the Cold

Good plot, but the writing is a little convoluted and old-timey. I can see how this inspires other spy novels though- the bones are good. The layers are there and the characters are believable. There's a fair amount of current-at-the-time politics that are harder to connect to now, but I can see why it's so widely recommended. It does a good job with moral ambiguity.