A haunting on F staircase in St. Thomas's College, Cambridge bitterly divides the college, and the Cambridge branch of the Psychic Investigation Unit (PIU) is invited to carry out an experiment. The main opponent of the plan, Professor Hawkridge, insists on being present when for the nocturnal investigation by the 'ghostbusters', only to drop dead of a heart attack. Now the college is really in trouble. The press has a field day, Hawkridge's widow...