In the novel, it's not in the theatre club room that's haunted. It's Elisha's room at the Duke's manor. Camilla discovers it when she goes on a week-long stay at Petro and Elisha's house to prevent the guardian sword from being stolen. Elisha was keeping an antique vanity mirror, which belonged to a dead actress of her favourite play. Ghost was trying to kill Elisha in order to take over her body, possess her, and start acting again. The event that would happen at the Duke's manor (regarding the guardian sword) is a major key into the progress of the novel.
In the novel, it's not in the theatre club room that's haunted. It's Elisha's room at the Duke's manor. Camilla discovers it when she goes on a week-long stay at Petro and Elisha's house to prevent the guardian sword from being stolen. Elisha was keeping an antique vanity mirror, which belonged to a dead actress of her favourite play. Ghost was trying to kill Elisha in order to take over her body, possess her, and start acting again. The event that would happen at the Duke's manor (regarding the guardian sword) is a major key into the progress of the novel.