During the Fall of Constantinople in AD 1453, the passage of a "four-dimensional fragment" through the Solar System imbues a prostitute with temporary powers to retrieve objects from enclosed spaces by exploiting the fourth dimension.

In the early years of the Trisolar Crisis, young aerospace engineer Cheng Xin is recruited by the Planetary Intelligence Agency (PIA) under its coldly-rational chief Thomas Wade.

Cheng wakes from hibernation, and is elected to succeed the aging Luo Ji, the inaugural Swordholder who established the dark forest deterrence.

Believing Earth to be lost, the two ships' combined crew activate Gravity's broadcast system as revenge against Trisolaris' treachery.

Several decades later, an unknown hostile alien race launches such an attack, which progressively collapses the three-dimensional space within the Solar System into two.

Cheng and AA arrive at DX3906's "Planet Blue" 286 years later, though the voyage passes quickly for them due to time dilation from the lightspeed travel.

There they encounter Guan Yifan, a civilian cosmologist on Gravity, who explains that the two ships' crew have founded several interstellar societies.

In their absence, Yun had visited Planet Blue to deliver "Universe 647": a Trisolaran-constructed self-contained micro-universe that exists outside of the conventional timeline.