The fictional world of The Three-Body Problem: a planet four light-years from Earth orbiting three suns in a system that is Alpha Centauri in all but name, whose civilisation has been destroyed and rebuilt more than two hundred times by the unpredictable motion of those suns, and which has therefore decided to leave.
Never shown directly
The novel gives two versions of Trisolaris and flags both as unreliable. The first is the pageant of pyramids, emperors and dehydrating populations inside a virtual reality game, which the book states is a recruitment tool. The second is a bureaucracy of consuls and listening posts in two late chapters, which the book states is one character’s imagination working on captured transmissions that contain no description of Trisolaran bodies. The aliens are never seen unmediated and the refusal is deliberate, which makes this a more disciplined treatment of an unknown intelligence than most of the literature this site handles.
The defector
The most direct human being in the novel is not human. The listener at Post 1379 has no name, appears for eleven pages, and has spent most of his life alone on a monitoring shift; when Earth’s message arrives he sends back a warning not to answer, because a beautiful world moved him. He is the single defector that the Dark Forest Hypothesis cannot survive, supplied by the author of the hypothesis inside his own first volume, and the whole plot follows from his breaking ranks.
What it is not
Fiction. The underlying three-body problem is real celestial mechanics, and a three-star system with a stable planetary orbit is not ruled out; the planet, the species, the fleet and the two-hundred-odd destroyed civilisations are invented.
Connections
The Three-Body Problem · Sophon · Dark Forest Hypothesis · Cixin Liu · Fermi Paradox