Earth will be invaded by the Trisolarans, an alien race, in four centuries' time. They have seeded Earth with sophons, subatomic particles that provide them with all Earth's information; only the human mind is unreadable. The Wallfacer Project selects four people to design secret defense strategies hidden from Earth and Trisolaris alike. Three Wallfacers are statesmen and scientists, but the fourth--Luo Ji, a Chinese astronomer and sociologist--is unknown, but he has a plan to stop the invasion.

Sequel to: The three-body problem.