This book actually had me worrying for Iain Banks's sanity. He wrote about psychopaths in a way that only someone with insider information could (I'm joking obviously, please don't sue me Mr Banks). As a psychology student, I find psychopaths fascinating. They are manipulative creatures who rarely tell the truth, so they are hard to understand. However, Banks manages to capture their personality perfectly. There isn't a single moment which feels weak or unrealistic, which is quite terrifying. If I was rating the book based on that alone, it would have been 5/5 without a doubt. His ability to enter the mind of a cold blooded murderer is almost unparalleled, and gives the book a chilling quality.
For me, the book was perfect up until the last few pages. There is a twist (which I won't reveal here) which made me laugh out loud. It was meant to be a serious, dramatic plot turn but I thought it was absolutely ludicrous. Up until that point the book was flawless, but the last few pages ruined it. Luckily the rest of the book was magnificent, so it still deserves 3/5, but I can't help but be disappointed.