Reclusive cop Dave wong (Daniel Wu) unwittingly saves the life of criminal gang leader Hon Kong (Nick Cheung) by donating his blood (Blood donation to dave and hon.), thus symbolizing that despite diametrically opposed outer appearances they are essentially made of the same stuff. The gang members hide their faces behind traditional demon masks when committing their violent crimes. During psychotic episodes Dave experiences his own demons within as he sets out to play off the gang members against each other, resulting in everyone's annihilation. It is then revealed that Dave was brought up by a high expressed emotion father in a socio-economically disadvantaged living environment. He witnessed his father's death inadvertently caused by the responsible policeman who resembled Hon Kong. As a young, innocent soul who had lost the father, he impulsively went on to take revenge, resulting in excessive guilt that predisposed the onset of psychosis later in his life. The event whereby he rescued Hon Kong reminded him of his suppressed memories as a child who had done wrong but trying the hardest to make reparation. Before his inevitable death, there was an opportunity for him to resolve his subconscious intrapersonal conflicts which was to have the courage to fix a mistake done.