The Dark Forest Is Another Mind-Bending Blend of Splashy SF and Serious Science

The Trisolarans discovered Earth during China’s Cultural Revolution, when a physicist sent a signal to one of our nearest stars. Helped along by humans not terribly impressed with humanity, and their overwhelmingly superior technology, they began quietly hobbling our technological advancement, softening us up for the coming invasion, due to arrive on Earth in 400 years.
The Dark Forest opens with the knowledge of the invasion spreading worldwide. Because it won’t arrive for generations, humanity’s reaction is muted at first, with a kind of can-do spirit emerging amongst the expected international squabbling. A plan to launc generation ships as a way of saving some remnant of humanity is dismissed as unethical and a risky resource drain. We’re all going to face this together. Yay!
But once the Planetary Defense Council is formed and the initial panic-slash-optimism burns off, humanity settles into a long, dark slog towards what seems like certain annihilation. Thanks to their 50-year lead time, Trisolarus launched sophons our way, sophisticated microcomputers capable of instantaneous communication between Trisolaris and Earth that have  wound themselves through the very fabric of our reality, monitoring our communications and interfering with physicists’ ability to take accurate measurements. Without experimentation, science will not advance, ensuring we’ll never close the technology gap before the conquering alien fleet arrives. Things look pretty dire—in addition to preparing for a hot war, the characters must also combat global dispair.
At the novel’s heart is the Wallfacer Project, considered our best bet against overwhelming technological superiority. Because the sophons can potentially hear any conversation on earth, and certainly must be monitoring all military tactics and planning, four people are chosen to plan our strategy with utmost secrecy. They are given almost unlimited resources, and left alone. Three of these elites are military or government folk of one stripe or another, and seem measured, sensible choices, but the fourth is the professionally lazy, undisciplined Luo Ji. Acting through human agents, the aliens immediately try to kill Luo Ji, which sparks another mystery: why is he the one they fear?

The answer lies in another question of theoretical science, this time dealing with developing a sociology of alien cultures and how they are bound to interact, theories Luo Ji never fully developed, because he’s kind of a hipster slacker. He is horrified by his Wallfacer status, and does what any good slacker would: he sets himself up in a castle, with a very good cook, and goes swimming a lot. Everyone nods knowingly like this is some kind of subterfuge, but he doesn’t really have an ulterior motive.
What’s fascinating about The Dark Forest is how the Wallfacer project mirrors your experience as a reader, strolling around the interior of the head of a man tasked with saving the world through the interior of his head: the plot’s action occurs largely within Luo Ji himself, and consists of a series of often startling thought experiments, coming from a perspective that is decidedly off kilter. (His invocation and relationship with a fictional character, for example, is both bizarre, and a great analogy for the complex push-and-pull between writers and readers.) The Dark Forest is much more brooding and introspective than The Three-Body Problem, the long, terrifying middle that trudges towards our uncertain end.