Joanne Harris' website has the following quote describing this book:
"The place is St Oswald's, an old and long-established boys' grammar school in the north of England. A new year has just begun, and for the staff and boys of the School, a wind of unwelcome change is blowing. Suits, paperwork and Information Technology rule the world; and Roy Straitley, Latin master, eccentric, and veteran of St Oswald's, is finally – reluctantly – contemplating retirement. But beneath the little rivalries, petty disputes and everyday crises of the School, a darker undercurrent stirs. And a bitter grudge, hidden and carefully nurtured for fifteen years, is about to erupt.
"Who is "Mole," the mysterious insider, whose cruel practical jokes are gradually escalating …? And how can an old and half-forgotten scandal become the stone that brings down a giant?"