Since the 1980s, Hong Kong cinema has given rise to a particular sub-genre around the figures of undercover cop which proliferate in movies with diverse themes and styles. The paper argues that its emergence is closely related to Hong Kong's peculiar colonial historical background and the corresponding cultural and political formation. As political and cultural metaphors, the figures and stories of undercover can enhance our understanding of the complexity involved in Hong Kong people's identity and subjectivity. They can also illustrate the changing structure of feelings both in the period of the late British rule and post-1997.