The title itself refers to the three-body problem in orbital mechanics.
Ye is taken into police custody and interrogated about her agenda about the ETO, about which she reveals possible classified information present on board the transport ship Judgement Day, which is disguised as an ordinary merchant ship.To collect the information about the Trisolaran world on board Judgement Day, the Chinese authorities work with international police and military organizations.Parts of the novel take place during the Cultural Revolution in China, as told through flashbacks.The family of a Tsinghua University astrophysics alumna, Ye Wenjie (叶文洁), was shattered when her mother and younger sister joined the Red Guards and her physicist father Ye Zhetai was killed by Tsinghua High School student mobs during a public struggle session.In 1971, Ye discovered the possibility of coding information and transmitting it using the principle of solar waves.
Gravely disheartened by the cruelty of humans and human society, she secretly sent a message about Earth's basic information and a request for help into space, without the knowledge of her co-workers.
Trisolarans developed the Sophon technology (a word amalgamation of Sophia, meaning "wisdom", and Proton, consisting of a supercomputer embedded into a single proton that had been unfolded from eleven space dimensions to two dimensions, programmed, and then refolded), with plans for two such Sophons to secure the complete lockdown of Earth's scientific research and development by giving out false results in particle accelerators.
In the meantime, they remained in contact with Ye Wenjie and gave her instructions to prepare for the coming of Trisolarans, while concealing their real motives.
Ye barely escaped persecution and was exiled to the countryside, where she got into deep trouble after commenting on Silent Spring, a banned book at the time.
She managed to find political refuge after being recruited into the "Red Coast Base", a top-secret military establishment commissioned by the communist government to establish contact with aliens.
It reveals the Trisolarans' plans in two phases: initially to halt science research and development through the Sophons' lockdown of particle physics, which has already begun, and eventually to send all of its galactic fleet to Earth to populate and colonize it in about 400 Earth years' time.