The Lucifer Effect
The book starts with a description of the Stanford Prison Experiment, where a group of students were split into 'guards' and 'prisoners' for a two week period - except that they took to their new roles so completely that the experiment was terminated after a few days. Zimbardo goes on to discuss other experiments showing how easily people adopt roles determined by what is going on around them, with a detailed description of his involvement in the Abu Ghraib prison abuse investigations.
Its a long book and I had worried that I might get bogged down in the story of the SPE before getting on to the discussion of other examples. In fact this was the most gripping part of the book, and it was towards the end of that I found myself flagging, in particular the long Abu Ghraib chapters. The last chapter on resisting situational influence seemed to be more about defining the word 'Hero'. In summary, the book has an important message, but don't feel that you have to read it all the way to the end.