Half a century after the Doomsday Battle, the Dark Forest Deterrence keeps the Trisolaran invaders at bay. It is an uneasy balance, but the infusion of Trisolaran knowledge has triggered an era of unprecedented prosperity on Earth. With human science advancing and the Trisolarans adopting Earth culture, it seems that the two civilizations can co-exist peacefully as equals without the terrible threat of mutually assured annihilation. But has peace also made humanity complacent? Cheng Xin, an aerospace engineer from the 21st century, awakens from hibernation into this new age. She brings knowledge of a long-forgotten program dating from the start of the Trisolar Crisis, and her presence may fatally upset the delicate balance between two worlds. The universe is a dark and dangerous place, devoid of mercy or sentiment. Will humanity reach for the stars or die in its cradle?