[3] Following the events of The Three Body Problem, humanity unites to defend Earth against the invasion fleet of the alien planet Trisolaris, which will arrive in approximately 400 years.

However, as sophons cannot surveil human thought, the United Nations appoints four "Wallfacers": individuals tasked with developing defence strategies known only to themselves, and are provided near-unlimited power to do so.

Three of the Wallfacers are renowned for their military, political and scientific expertise, but their secret strategies are ultimately exposed by Trisolaris' agents, the "Wallbreakers".

The fourth Wallfacer is the obscure sociologist and ex-astronomer Luo Ji who, despite being less qualified, is chosen because he is the target of the only assassination order ever issued by Trisolaris.

Amidst the ensuing panic on Earth, Luo resumes his Wallfacer role and dedicates his efforts on a seemingly ineffective defence strategy, which is actually a secret ruse to overcome the Trisolaran jamming of cosmic broadcasts.