Narc (2002)

Nick Tellis is a recovering drug addict. But staying clean is not so easy for this Detroit narcotics officer when the police department reinstates him in order to investigate an elusive 'narc' squad homicide. After a rookie cop is mysteriously killed in the line of duty, the police department teams Tellis up with the dead cop's partner--the volatile Lieutenant Henry Oak--to solve the murder. Soon the two of them find themselves crawling through the mean streets of Detroit. Their probative investigation leads them through filthy drug dens, crack houses, and alleyways to track the killer, but these all too familiar surroundings plague Tellis like a nightmare. As Tellis gets closer to revealing the truth behind the murder, he finds himself in jeopardy of losing his family, his dignity, and his life.