This is an important book, as many of the official reviews and comments have said, and the content and relevance are both excellent. However, it's worth saying from the outset that it is no light read. This is true in terms of the subject matter, but also in terms of the small font and exhaustive writing style. This is a thorough book that covers its message to absolute completion, and makes no attempt to skip over the detail of that.
Roughly, the book is split into 3+1 sections. I say 3+1 instead of 4, as the 4th is almost an appendage rather than a dedicated section in its own right. After a brief introduction, the book dives directly into its main subject matter: an exhaustive and minute-by-minute account of the Stanford Prison Experiment. It is by far the most detailed account I have read on the subject, perhaps not surprisingly so when you consider that Zimbardo was the principle orchestrator of the study. I won't go into detail of the accounts, as that would spoil the book, but there are detailed descriptions of every nuance and situation encountered.
Having consider the experiment from start to finish (or strictly speaking, to abortion), the second part of the book then reflects on the social psychology lessons learned from it. Alongside other famous contemporary experiments, such as the work by Stanley Milgram on obedience to authority, a picture is drawn of how situational forces are much stronger at influencing our behaviours than we care to admit. This is, of course, the core point of the book.
With the account given and the social and behavioural analysis complete, the book then moves to Zimbardo's own experiences as an expert witness in the trials of guards involved in the Abu Ghraib scandal. As would be expected, Zimbardo's core point is that the terrible acts committed are not--as the official explanation states--the work of a few bad apples, but instead were the result of systemic and situational failures throughout many areas. He draws on his research through the Stanford experiments to conclude that anyone in that situation may have acted in the same way. This is not an excuse, but rather an explanation.
Lastly, the book considers the reverse, whether situations can also generate heroes, and what that might say about them.
Personally, I found the first and second sections the most enlightening and interesting. The implications for Abu Ghraib, whilst damning, are somewhat academic since the sentences have already been passed and the blame apportioned. In fact, Zimbardo himself admits on a few occasions that he feels his expert testimony wasn't really taken seriously. As such, the third section turns into something of an exercise in creating a water-tight soap box for his now incarcerated clients. Whilst his conclusions are compelling, he is somewhat preaching to the choir, and the sheer quantity of his "evidence" can be overwhelming. I found that I didn't need to read and dissect tens of testimonies and statements to agree with his core point, and I have to confess that I eventually skipped much of this section.
Similarly, with the final section, whilst an interesting muse, I did not feel that there was anything of a revelation in nature. Because of the length of the book (deceptively so because of its small font size and tightly packed paragraphs), I think that it could arguably be split into two books, and for me is the account of the Stanford Prison experiment and the subsequent psychology analysis which is important, less so the political agenda.
Buy this book if you are fascinated in the equality of people, and how the saint can become the sinner, the freedom fighter the dictator. It shows how we are all capable of incredible good and incredible evil, and the route we take is less of our own intrinsic nature and more a product of our circumstances.