Ayi (played by Julian Cheung) is a special police officer. While on duty, he accidentally discovered that the boss of a company had close ties with Korean radicals and was planning to smuggle weapons from Taiwan to Hong Kong. Ayi quickly got the intelligence and started a fight with them. Unexpectedly, his leader Sheng (played by Anthony Wong) was killed in the hail of bullets, and the main criminal Jin also escaped. Later, Ayi transferred to join the ranks of G4, with the mission of protecting the safety of government officials. He worked hard every day and had no time to take care of his girlfriend Kelly (played by Carman Lee), and a rift appeared in their relationship. But Ayi did not forget to avenge his good teammates back then. At this time, Ajin appeared again and planned to join forces with Korean elements again. Ayi was determined to seize the opportunity to avenge his friends and bring the criminals to justice.