By Nightfall, by Michael Cunningham. I loved it so much I was compelled to review it in a hub. The main character is having something of a mid-life crisis and it made me really think about my own life, the mistakes I have made, and what kind of changes to my life I would like to make. It made me think about the danger of just becoming complacent, and how often we just find ourselves going with the flow without stopping to assess and reevaluate things. It was a great book, strongly recommend it!