Where to begin? This books has had an almost mystical position in my life - my dad loves it, and the BBC miniseries, and somehow I always accepted that it was a great book without ever thinking to read it. When I heard the new movie was coming out, I decided it was time, and I was a little worried that it wouldn't be as good as I'd always heard, but that worry was completely unfounded. It was amazing. I've been slowly working through Le Carre's novels, and I've enjoyed the other three (his first three) a great deal, but this one displayed a whole other level of complexity and skill. It was dense, and took a very long time for me to read, and I already want to reread it to pick up on the things I missed the first time, but that came across as a deficiency in me, not the book. I am not as smart as Smiley. I accept this.
A quick word on plot, for those of you who haven't seen the miniseries or the new movie* yet: George Smiley, retired spy, is secretly brought in to find out the identity of a mole that the Russians have placed in the British secret service. The story has several layers and puzzles and knots, and some amazing characters, and the writing is exquisite. If you haven't read Le Carre, you might want to try his first, Call for the Dead, as a kind of warm-up, but if you like spy stories, you must read this at some point.
* The miniseries and new movie are both extremely good and I highly recommend them!