Mary Giordano (Alicia Silverstone) is a bright, intelligent student who attends a Catholic school in Burlingame, California. She is about to graduate in a few weeks. She is addicted to mystery novels and detective magazines, hence the title of the movie; this inspires her to do her own detective work, as she has aspirations of becoming a police officer herself. When she starts snooping around on the case of murdered teenage girls, it gets her into difficulty with her mentor, Detective Jerry Guinn (Bill Nunn). Guinn knew Mary's father who was a cop and he was killed in the line of duty. He is worried about Mary and doesn't want her in the field. Mary teams up with police cadet Tony Campbell (Kevin Dillon) to investigate, and as the two work together to find the murderer, they seem to have feelings for one another. But the closer Mary gets to solving the murder, the greater the danger of being the next victim to which she exposes herself. Mary almost figures out that Tony is the murderer the whole time.