I listened to the audiobook on Hoopla, narrated by Gildart Jackson. It was missing the entire final chapter, which I only discovered when the summary I read after didn't fit what I heard at all. I finished reading it on Gutenberg.

The evolving nature of the story as it progresses is brilliant, even if it may be frustrating to find yourself not reading what you thought you were. What starts as a spy thriller turns out to be nothing of the sort (and yet it has influenced the entire spy thriller genre). But that's reflective of the point.