With the Trisolaran invasion fleet four centuries away, humanity deploys the Wallfacer Project—four individuals given unlimited resources to develop secret deterrence strategies entirely within their own minds—while the Sophons monitor all human communication. One of the Wallfacers, sociologist Luo Ji, must discover why he was chosen and what the Dark Forest theory of the universe truly means. A philosophically massive novel about civilization, survival, and cosmic indifference.