One rainy night, a rescue brings food delivery rider Lu Chen into a life-bound pact with Luo Yuan, who died ten years ago: she can remain in the mortal world only as long as he stays alive. From a corridor with no doors to a piano that plays by itself in the dead of night, the hidden side of Wujian City gradually emerges. As Luo Yuan's memories awaken, an old fire case that was buried for years points to Jingchuan Group and a missing underground second floor. One is a young man whose future was ruined because he saved someone; the other is a rescuer branded an arsonist. From mutual suspicion to joining forces in the investigation, this time they must recover not only their chance to survive, but also the truth that was stolen from them.