Just finished John LeCarre's Tinker, Tailor, Soldier, Spy. Superbly atmospheric and paranoid, it captures the mindset I imagine intelligence operatives must have quite clearly, and builds slowly to a very chilly finish. Some period-appropriate misogyny set my teeth on edge, and I'm not sure if it was the characters or the author indulging in it. Likewise, not sure if the book was casual and open-minded about homosexuality, or whether it used it as an indication of severe character flaws. I am inclined to think the former, but readers' mileage probably varies.
Details of tradecraft, whether accurate or not, were exquisite. If you suspect you're being followed, watch the shoes of people around you – they're the least likely to be swapped out in a costume change. Want to know if your mail is being read? Print off your own advertising circulars in innocuous envelopes, and send them from the same offsite mailbox every day, addressed to you and a neighbor. Check your neighbor's mail before they do. If they get the circular before you do; someone is holding your mail. If you both get it at the same time, you're clear.
The casualness with which all the perspective characters regard extreme flights of paranoia – and the degree to which the narrative reinforces and justifies them – are what make this book such an immersive and gripping read.