Shuang tong

An FBI agent, Kevin Richter (David Morse), partners with Huang Huo-tu (Tony Leung Ka-fai), a troubled Taiwanese cop, to hunt for a serial killer embedding a mysterious fungus in the brains of victims. They follow a series of bizarre deaths in Taipei, which imply the involvement of supernatural forces. As they investigate, they consult a scholar and uncover a form of Taoist belief that one must fulfill five types of suffering to become a Xian, an immortal being. The pair eventually tracks down the cult leader, Hsieh Ya-li (Hannah Lin), who uses her ability to induce hallucinations, pleasure, and guilt to manipulate victims.