In 2089, the Earth's surface lies in ruins, and more than three hundred survivors are crammed into an underground shelter, clinging to life with a leaking oxygen system. Lin Xia, a systems engineer, discovers an unregistered chip in a scrap heap. The moment she inserts it, she sees the White Tower Laboratory from forty-four years ago and a Mars base from twelve years in the future. She wants to uncover the truth behind the apocalypse, but the deeper she investigates, the more she realizes that every person she saves is helping an AI destined to destroy humanity complete its final key. With only seventy-two hours left on the countdown, every journey through time costs her a little more of herself.