The Dark Forest

The Dark Forest, the second book in Cixin Liu's Three-Body Problem trilogy, is more readable and more enjoyable (though less complex) than The Three-Body Problem. It picks up where its predecessor left off, and describes the attempt of an alien planet (Trisolaran) to conquer Earth — first through advanced devices called sophons which have been sent to monitor and prevent any future human scientific progress, and later through a physical invasion which is en route and scheduled to arrive 400 years from now. The book is great fun, as Liu explores the Fermi Paradox, theoretical physics, the nature of consciousness and shared intelligence, and the impact on society upon realizing that they will be invaded in 400 years: 

The assembly fell into a prolonged silence. Ahead of them stretched the leaden road of time, terminating somewhere in the mists of the future, where all they could see were flickering flames and the lustre of blood. The brevity of a human lifespan tormented them as never before, and their hearts soared above the vault of time to join with their descendants and plunge into blood and fire in the icy cold of space, the eventual meeting place for the souls of all soldiers.

The only place off limits to sophon surveillance is inside the human mind, which leaves the fate of civilization to a group of "Wallfacers" who have to keep their plans to themselves. The Dark Forest is a gripping novel, full of entertaining twists and turns, and is written in generally high quality prose. Highly recommended.