Night Caller (1985)

A family guy cop (Melvin Wong) goes deep into a case and gets involved with a deranged killer. His partner and friend (Philip Chan) along with a new protégé Porky (Pat Ha) take over the case and look for his missing partner (who's "enjoying" the twisted company of the killer. Can Inspector Chan and Porky find Melvin before he becomes the latest victim of the psychotic killer?