After Wang Miao logs out of Three Body at three in the morning, Shi Qiang urgently summons him to the Criminal Division. There Wang meets Xu Bingbing, a computer specialist, and unexpectedly finds Wei Cheng, Shen Yufei's withdrawn husband. Wei says his life is in danger, and at Shi Qiang's request he explains the long history behind his connection to Shen and to the three-body problem.

Wei describes himself as a gifted but chronically lazy mathematician whose unusual intuition let him grasp formulas and numerical patterns almost instantly. After drifting through school, higher education, and an unsuccessful academic career, he withdrew to a mountain temple seeking a quiet life. There, while trying to calm himself by imagining matter in empty space, he mentally explored universes with one, two, and then three spheres. The third case fascinated him because its motions became wildly complex, and this experience awakened a genuine passion for mathematics. Wei concluded that the three-body problem required not pure analytic elegance but a new computational method.

Wei says that while he was filling ledgers with calculations at the temple, Shen Yufei discovered his scratch work and immediately recognized his approach. She offered him computing resources and drew him away from the temple, despite the abbot's ominous warning after hearing Shen pray for Buddha to save 'my Lord.' Over the following years, Shen supported Wei with money, computers, and travel so that he could pursue an evolutionary algorithm for the three-body problem. Their marriage, Wei explains, was practical rather than loving: Shen cared only about his research, and he cared only about continuing it.

In the present, Wei reports that his peaceful life ended when an anonymous caller threatened to kill him if he did not stop his research. Soon after, Shen herself woke him in the night with a gun and threatened to kill him if he did stop, telling him that solving the three-body problem could save the world and abandoning it could make him a sinner. Shi Qiang realizes that Shen's apparent illegal possession of a firearm gives the police grounds for an immediate search, so he takes Wang, Xu, Wei, and officers to the house before dawn. On the way, Xu quietly tells Wang that Three Body is being monitored by Information Security, that its servers are abroad, and that it seems far more than an ordinary game.

When the group arrives, they hear suspicious noises upstairs and rush in. They find Shen Yufei shot dead in a room full of blood, with multiple bullet wounds and a gun nearby. Shi Qiang chases toward another room and glimpses a fleeing suspect escaping by car. Questioned at the scene, Wei reveals one more important fact: he overheard Shen arguing with Pan Han, who spoke of divisions inside their organization between Adventists and Redemptionists and accused Shen of trying to prevent 'our Lord's' arrival. Before Wang leaves, Wei gives him a disk containing his three-body algorithm, urges him to stay away from what is coming, and bleakly suggests that the world is nearing a catastrophic change that neither police nor prayer can stop.