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 threatens to sue, and St. Thomas's is swamped with tourists who want to sleep in the 'haunted' room.' Sir Joseph Zuylestein, the College Master, asks Dr. Nathaniel Gye, a parapsychologist, if he can make some discreet enquiries with a view to closing the whole sorry business — the affair could not have come at a worse time, as St. Thomas's is about to accept a major donation from a publicity-shy billionaire. But Zuylestein has another reason for wanting everything hushed up — he has received anonymous letters indicating that the undergraduate Tom Sutton, whose unquiet spirit supposedly haunts F staircase, did not commit suicide ten years earlier, but was murdered.