On Juvenile Watch, working the day shift, Joe Friday reports to the local Junior High School. Mr Chase is at the end of his rope with 21 incidents of students being knifed. Joe and Ben ask questions to look for patterns in the activity. Before the cops can leave, another attack takes place.
Accompanied by policewoman, Lorainne Jensen, the cops gather the victims to see what else they might learn. Joe and Ben are escorted through the school by Jim, who shows them the lay of the halls where attacks have taken place. Just when a plan is developed to stakeout the halls, and keep girls safe, another attack goes down. In sorting the raw data, one name rises to the top of suspects, Jim Traverse.
Jim seems to be a loner with few friends. He seems to be bashful but has been known to hurt girls he dates. Joe notices that when Jim is on hall patrol, no attacks take place. Jim is overly helpful, and claims to have an interest in police work. Making a show of including the teen in some high tech police work, Joe lures him into letting down his guard.
Under the heavy weight of his own conscience, Jim cracks to confess all.