Mary Giordano is a bright, intelligent student who goes to a catholic school. She also has an addiction to mystery novels and detective magazines (hence the title of the movie), which inspire her to do her own detective work. When she starts snooping around on the case of a murderer of teenage girls, it gets her in hot water with her mentor Detective Jerry Gunn. But it also starts a team up with police cadet Tony Campbell. The two work together to find the murderer. But the closer Mary gets to solving the murder, the more danger she puts herself in of being the next victim.