Ran Fangxu and He Xiaohe run into the property manager, Qian Dajun, in the underground parking garage. Qian Dajun claims he is fixing the wiring and carries away an electrician's tool bag. Ran Fangxu uses the Tremaux algorithm to sweep the building and brings He Xiaohe up to the rooftop, where they run into Qian Dajun again.