He explains how our brains work, how the neurons interconnect, how memory is created and stored, and then finally how the brain creates a narrative around these memory to give it a sense of continuity and overall framework. This 'self' is, according to Hood, a fiction that may change dramatically depending on the situation (eg work vs private environment) or the different phases in life. The same holds true for free will, which is also a conscious creation of brain cells and neurons at work in the background, and the post hoc rationalisation is nothing more than a narrative for what's happening unconsciously. A quite shocking statement for us who so strongly believe in our own rational powers and strong personalities (including your humble servant).
Yet Hood's explanation, his rigorous documentation of own research and of cases presented by other scientists is quite compelling, especially now that brain scans can demonstrate that our brains decide several seconds before we make a conscious decision.
Many of Hood's examples and extreme cases were already mentioned in other books on the same topic, such as the ones by Oliver Sacks or Daniel Kahneman, yet at the same time, it's good to have them again in a very accessible and even entertaining book with a very comprehensive overview of today's cognitive science.