Sergeant Xu Dahu broke several major cases, but his independent style led to conflicts with his supervisor, Li Pengfei, and he was transferred. Dahu resigned in frustration but was encouraged by his girlfriend, Ho Yuk-kam, to start a private detective agency. While taking the police officer's exam, Ho Zi-wai became friends with Li Chang-zi, who was frequently praised and promoted. Zi-wai felt unfairly treated and eventually left his job to join Dahu's detective agency. While investigating a kidnapping case, they discovered more secrets and illegal activities involving Pengfei. They used a citizen's arrest empowered under Article 101 of the Criminal Procedure Ordinance to bring the culprit to justice.