A haunting in St. Thomas''s College, Cambridge bitterly divides the college, and the Cambridge branch of the Psychic Investigation Unit is invited to carry out an experiment to settle the unrest. But when the main opponent of the plan, Professor Hawkridge, insists on being present for the nocturnal investigation and suddenly drops dead that very night the press has a field day and the college needs answers

Sir Joseph Zuylestein, the College Master, asks Dr. Nathaniel Gye if he can make some discreet enquiries with a view to closing the whole sorry business. But when they receive some disturbing anonymous letters that seem to prove the undergraduate, whose unquiet spirit supposedly haunts St. Thomas''s, did not commit suicide ten years earlier, but was murdered, the case suddenly becomes altogether more serious...