I knew the concept of this book strangers on a train agree to commit a murder for each other before reading it.  What I did not expect was how insidious and obsessive Charles Bruno was, his state of mind and taunting actions throughout the book was very interesting, a psychopath absolutely but with a depressive lonely edge to him.  Patricia Highsmith does an amazing job of making even him worthy of pity.  There are some well known (psycho) tropes but instead of feeling overdone Bruno's hatred of women, his weird relationship with his mother and his homoerotic fascination with Guy all adds menace and horror to the atmosphere.  It is easy to see how Hitchcock made this into an amazing psychological thriller film noir, the writing is so good as well as the characters and plot.  Guy was the ultimate guilt infused person, his experience of committing murder, and knowing someone who had committed murder and trying to live with it is the thread of strain throughout the entire novel, you are left on tenterhooks waiting for it, for him to snap.  And this weird connection between Guy and Bruno, hatred and loathing but unable to leave each other alone is a very interesting dynamic.  Weirdly throughout you want Guy to be able to get away with it while you want Bruno to get caught.  Amazing book, one of my all-time favourites.