Death’s End by Cixin Liu
Death's End is the conclusion to the fabulous Remembrance of Earth's Past trilogy. The Trisolarans and Earth are basically at a stand-off, thanks to events in book #2. The "peace" is working well, but of course can't last. Enter Cheng Xin, our main character for this installment. She's a regular, intelligent woman who hops through time, thanks to hibernation, making bad decisions. Maybe that's harsh. She makes decision consistent with her character, but she was more or less put in charge of humanity's fate twice, which seems a little unlikely. it works within the plot, but the story works hard to get you there.
Death's End is a tough book to talk about. On the one hand, it's amazing. The scale in time and space that the author is working with is enormous and he makes it believable without making it too easy. There's a lot of science here, I feel like it was explained well enough for me...