Mad Detective (Chinese: 神探; pinyin: Shen tan; Cantonese Yale: Sun taam) is a 2007 Hong Kong crime thriller film produced and directed by Johnnie To and Wai Ka-Fai, and starring Lau Ching-Wan as a police officer, who decides to come out of retirement to help a rookie cop (Andy On) solve a murder case, involving a missing colleague and a suspected cop (Lam Ka-Tung) suffering from a form of multiple personality disorder.