The Rural Patrol Team has found some balloon debris in a tree around the hilltop. HANG and LAI go to the university to see POK. They bring along the climate data recorded on the day of the acid attack so that POK can have a clearer picture for analysis. LAI notices that there is something wrong with ON and SHEUNG. For the sake of HEI, ON would like to team up with his friend to tender for a catering contract with the university. Knowing that her brother and sister-in-law are in need of capital for the project, LAI offers to lend them money straight away. Based on POK’s analysis, the police decide to conduct a large-scale questionnaire survey in Tai Kok Tsui. LAI arrives at a rooftop squatter, where she meets a young man called CHEUNG HON-CHEUNG. After the onsite investigation and a thorough analysis of the survey data, the Regional Crime Unit identifies CHEUNG as one of the prime suspects… The case is finally solved……