Out of Bounds Taggart : Season 14 Episode 4

Jardine investigates a triple murder at an exclusive boys' boarding school. In each case the victim is a disciplinarian schoolmaster. Eventually he discovers a further link in that several years earlier they had all been prefects who bullied a boy called John Chisholm. John Chisholm has now come back to get revenge, though not in the form that his victims would have recognized.