Detective Li helps him get out of the jam, and he, in turn, helps her track down the elusive killer. Li develops a romantic interest in Big, but he seems to want to avoid her. Pressed to explain himself, he eventually reveals his bizarre and tragic past.

Big was a kung fu monk until a woman friend of his was murdered years ago, sending him into an uncontrollable rage, during which he inadvertently killed a sparrow. After meditating over the bird's corpse for a long time, Big developed the ability to "see karma." He can look at any animal (including people) and see what they did in their past lives. When he looks at Detective Li, he sees that in a former life she was a brutal Japanese soldier who murdered many. Even though she's a good person, she still carries that soldier's karma, and Big believes she'll eventually have to die for his crimes.

Despite his misgivings, he finds himself increasingly drawn to the persistent young cop. Running on Karma was directed by the team of Johnny To and Wai Ka-fai (PTU). The film was shown at the 2004 edition of Subway Cinema's New York Asian Film Festival.