Building Inspector Tony (Tony Leung Ka Fai) investigates an old abandoned building in a deserted plant site and falls victim to a restless demon, who wants to resurrect into Tony's body. However, the spirit of a young woman (Rosamund Kwan) suddenly appears, saves Tony, and accidentally sucks some of his life force, thereby, sharing his feelings and emotions. The ghost falls in love with Tony, but he wants to use her to help him woo his gorgeous colleague (Ellen Chan).

A look at the SDU in the Royal Hong Kong Police Force - how members are selected, how they are trained, their lives, what they think, the relationships between SDU members and their friends and the pressures they face.