Based on a book by Hong Kong filmmaker Pang Ho-cheung, Fulltime Killer protagonist O is a hitman being challenged by new hotshot Lok Tok-wah. O has lived a life of seclusion as the number one hitman in Asia. The woman living at his contact address is captured after O foils a set-up by his boss. He then goes on the run whilst trying to fend off his adversary. The last part of the movie focuses on an Interpol detective's attempt to write the story of Tok and O.