Love at Large (1990)

A down and out private detective (Berenger) is asked by a beautiful woman (Archer) to follow her lover (Young) because she thinks he may be planning to kill her. Due to her poor description she's in danger. He ends up following the wrong man, but discovers the wrong man has some sleazy secrets himself. Meanwhile another detective (Perkins) has been hired to follow Berenger, and they eventually decide to work together to find out what is really going on.