A group of teachers must defend themselves from a gang of murderous kids when their school comes under siege after hours. In England, the teacher of the Wittering College Robert Anderson is hit on the face by a student and is forced to take three months vacation to be not sued by the parents of the kid. Robert is affected by the incident and a couple of months later, he is emotionally disturbed, alcoholic and separated of his wife Helen. Their daughter Kate lives with her mother and has classes with Robert, but she does not respect her father. The principal of Wittering College, Sarah Balham (Ruth Gemmell), loathes Robert and wants to get rid of him, but the Union does not allow her to fire him. When Robert reads about violence in another school, he sends a memo advising the employees of the school and he is considered paranoid and delusional by everybody. One day after hours, Robert notes some strange movements outside the school and he advises the security guard James that does not give much attention to the discredited Robert...