Quite late in the novel Conrad's Fate, while everyone is getting ready for the first big social event that has been hosted there during Conrad's term as a trainee footman, odd events begin to happen in the house.  Things are moved from one place to another.  A large rubber ball is seen bounding by itself in the hallways, or bouncing slowly down the main staircase as the staff is practicing its entry positions for grand entrances of guests.  Eventually both ghostly events as well as normal probability shifts are being blamed on the Ghost, but it's not until capable people in charge of things start investigating that its real identity is discovered.