The Chinese government put a very secretive extraterrestrial search program in place. It happens that the Trisolarian civilization receives the Earth transmission and replies. Being in a three body system, this civilization doesn't have a stable rhythm and cannot predict it. Stable eras allow them to progress but unstable ones forces them to hibernate by dehydrating their body and waiting for the next stable era. For this civilization, finding a better planet is a matter of survival.
Being exhausted by the human behavior regarding wars, conflicts and environmental destruction, a group of humans establish and maintain the contact with this trisolarian civilization, hopping that it would be better than humans. In the end, we learn that the Trisolarians are way more technically advanced, totally disregard humans and only look forward to colonizing the Earth. They start an expedition to travel to Earth and use their technology to prevent any technical progress on Earth as a way to ensure their supremacy when they will arrive.
It was pleasant to read, but I wasn't really hooked either. This is stupid, but having Chinese names makes it harder to remain who's who.
The reaction of the humans who want the Trisolarians to come is interesting. They mostly see the bad side of the humans and bet that this new civilization cannot be worst that the humans. It resonates with a similar behavior in "Ministry for the Future" where a group of people is so desperate that it starts a terrorist group to do something. It shows that people can get very extreme when they are desperate.