"The Dark Forest" by Cixin Liu

The second book in the "Remembrance of Earth's Past" trilogy starts a few years after the previous book ends, but most characters (except Da Shi, who is the real main protagonist of the entire trilogy) are new.  Since humanity is desperate to find a way to escape destruction coming forward by the Tri-Solarian fleet, the UN creates the "Wallfacer" project, four people endowed with (almost) unlimited powers to create strategy that will win over the Trisolarians.  The wallfacers (old Chinese terms for meditators) do not have to reveal their strategy or planning to anyone, as the sophons can read any communication except the human thought - trisolarians having exposed thoughts and no need for additional communication aparatus. 

Of the four Wallfacers, only Luo Ji, is completely unknown on a world scale, and initially he uses the Wallfacer project to get himself a dream property and find the girl from his dreams, who he has loved ever since he attempted to write a novel about her.  He is stunned when Da Shi finds exactly the girl from his imagination and he takes her to a private, night tour of the Louvre, where they fall in love in front of the Mona Lisa.  However, after five years she is taken from him, together with their daughter, in order to force him to work on saving the Earth.

Luo Ji is important because Ye Wenjie, one upon a time, tells him about "Cosmic Sociology" from which he extrapolates his "Dark Forest" theory of the universe.  Which is the one thing Trisolarians fear most.  Basically, the "Dark Forest" theory says that all intelligent species of the universe are akin to stealthy hunters in a dark forest, where the discovery of the position of each hunter causes any other hunters to immideatly kill him, less their own positions are discovered and they themselves murdered.  The "Chain of Suspicion" theory logically concludes that any other action, except outright destruction of another technological race, is inferior in game-theory concepts, and does not lead to an optimal solution (unlimited survival).

Luo Ji uses the sun to project a spatial map chunk which can be used to identify a star 50 billion years away, with the intent that some intelligent species will receive the transmission and destroy that star system, according to the cosmic sociology and the "Dark Forest" theory.  Then he goes into hybernation and sleeps for 2 centuries, when humanity, after going through the "Great Ravine" when half of the Earth's 7 billion population has died, has developed underground cities (the surface is almost destroyed by ecological disasters), space cities and space fleet of 2,000 ships (Trisolarians have 'only' 1,000) which posses planet-shattering weapons and can reach 15% the speed of light (Trisolarian ships can reach 'only' 10% of the speed of light).  The Wallfacer project has been forgotten, since the new fleet is believed to be a sure winner in any space battle and Luo Ji becomes an ordinary citizen.  Da Shi is serendipitously awoken at the same time and saves Luo Ji's life several times.

However, the Trisolarian forward probe, one teardrop shaped space-vessel, 1/10,000th of the mass of a Trisolarian warship, arrives first to the Solar system and the entire Earth Space Fleet goes to await it.  This is when the book becomes one of the best science fiction books ever written and the next pages to the end are dense, suspenseful and full of revelations.