Late Night Cleaning: I Can See the Evidence of Incrimination

Ji Yuan worked the night shift as a cleaner for five years, and the floor he mopped could go around the office building three hundred times. Until three o'clock in the morning that day, the mop stopped on the carpet in the boss's office on the 51st floor - fluorescent drag marks extended from the desk to behind the bookshelf. System activation: [Trace Tracing] - Source of blood stains: Type O, female, missing within 48 hours. Secret door. Secret room. Dried dark red. Panel prompt: The pollution source is still active. Someone came into this room last night. From that day on, Ji Yuan no longer wiped away dust. He wiped out the city's secrets.