Police detective Ha Chun-Chi (Shu Qi) is investigating a rape and murder that took place in a mysterious forest that has also been the scene of many suicides. The main suspect in the murder case is Patrick Wong (Lawrence Chou), but he denies committing the crime. Ha's investigation leads her to botanist Shum Shu-Hoi (Ekin Cheng), who has been experimenting with plants from the forest. Shum's girlfriend, May (Rain Li), feigns interest in the forest to gain information for a tabloid television show she works for. Shum's experiments reveal that the plants can act as witnesses in the murder case, and sets up a re-enactment of the crime in the forest, where the plants will act as lie detectors.