Part two of Cixin Liu's increasingly dark "Three Body Problem" series.
Liu has a theory as to why our galaxy appears so empty of life. Species are hiding from each other. When a species does announce its self to the galaxy, a nearby more-advance and more-paranoid species will destroy it. Slowly our galaxy fills up with paranoid civilizations hiding from each other.
The book then is about earth's first encounter with an alien civilization, and how wrong that goes.