Francis Pilkington, an English teacher at St Cuthbert's School, gets a new toy, a Commodore 64 computer. He uses it to solve some of the petty misdemeanours of the pupils, a mess in the boy's toilets, a missing Rolex, stolen lunch money, but, one day, he is called upon to use his fledgling computer skills to solve a much more serious crime, when Anthony Holborne, a candidate for the headship, is found dead by the matron the day before the interview...