I don't really know why I picked this book---probably the fact that it was quite visible in the bookshop! And... with so many weird interactions online, who can resist understanding (or trying to) "trolls" and people whose actions do not make any sense?
This book does a good job of explaining the difference between the empaths (i.e. the "normal" people) and the sociopaths. It gets a bit dense and boring in places, and there's also many parts which feel unresolved, as if the author got tired and didn't want to continue talking about it.
Not a book I think will be coming back too often, but good to get an idea of how others think. I've already put in practice its "litmus test" to detect is someone is actually lacking all empathy or is just an idiot, and it seems to work! (tip: it's about criticising something they've said---sociopaths won't care much as long you're not in their way, whereas empaths/cretins might get really upset that you're criticising them).