Jonas was the caretaker of the House on Haunted Hill, alongside his wife, for years. When Frederick Loren rented the house for a haunted house party, Jonas and Mrs. Slydes were to leave at midnight and lock the only door out; trapping the guests inside for the night until they unlocked the house at 8 AM.
Shortly before midnight, when Nora Manning gets lost in a dark hallway, Jonas grabs her and begs her to come with him and Mrs. Slydes, "before he kills you." However, Nora mistakes him for a ghost and runs off. Jonas and Mrs. Slydes follow Nora down to the living room, where Frederick explains the misunderstanding to Nora.
Frederick then offers the guests a choice to leave at once with Jonas and Mrs. Slydes, or stay locked in the house for the night. But before any of the guests can choose, Jonas and his wife for some reason leave a few minutes early, locking Frederick and the other guests in for the night.