A 26-year-old female programmer living alone, Xiao Li, has long suffered from the noise torture of 68-year-old elderly man living upstairs, Uncle Zheng, knocking on the floor in the middle of the night. From angry complaints to going up to confront him, she unexpectedly discovers that Uncle Zheng has Alzheimer's disease. As Xiao Li gradually learns the heartwarming secret behind Uncle Zheng's floor knocking (a secret code with his deceased wife), the two build an intergenerational friendship that bridges the generation gap. However, when the noise suddenly disappears for three consecutive days, Xiao Li pries open the door, only to face the cruel reality of Uncle Zheng's lonely death.