Arliss Howard plays a baby-faced undercover cop, posing as a high school student. Howard is investigating the murder of a teacher, a task made difficult when his own brother (Loren Dean) becomes the primary suspect. Meanwhile, the ersatz student falls in love with Alexandre Powers, the daughter of the school's gym instructor. Before long, Howard is having trouble separating his "real" self from his fictional persona: he event develops a crush on home-room teacher Suzy Amis! Director Martha Coolidge and scriptwriter A. Scott Frank seem to be having a lot of fun pushing the credibility envelope in the amusing but unnecessarily convoluted Plain Clothes.