This is a very hard book to read. A lot of information and even more contemplation. This is long essay about the origins of totalitarian system from the perspective of the author. In his opinion it goes back to Plato and his notion of a the closed (tribal) society, where the main objective of society is the collective, the city state.

The second part is about Marx mostly. Popper thinks Marx identified the right problems, had the right intentions but prescribed a terrible medicine.

The other very interesting point is with utopias.

Utopias are not just dangerous because there is no such a thing. There very well could be. True, accepting our imperfection as a human race is a much more mature thing, but that is not the biggest issue here.

Utopias are dangerous, very dangerous, because we don't know what makes societies work. We might change something and it can have 2nd, 3rd order effects that we did not thought of. We are unaware of our lack of knowledge.

Utopias require big changes. The bigger the change the possible damage done to society grows. Not in a linear fashion. That makes some changes irreversible.

The solution is something Popper calls peace meal engineering where thing go in a trail and error way. Keep the errors small and reversible. So when things go wrong (and most of the time they will) the damage is repairable.

Highly recommended if you are interested in individual societies and freedom in general.