Final answer:
Miss Brent becomes disturbed and anxious while sitting alone in the dining room, likely due to the unsettling atmosphere.
Step-by-step explanation:
Miss Brent suddenly becomes disturbed and anxious while sitting alone in the dining room.
Before this event, Miss Brent appeared calm and composed. She brewed a cup of tea and sat down in her rocking chair to relax after the emotions of the evening.
It is likely that Miss Brent behaved this way because she sensed that something was not right. The description of the abandoned and deserted dining room, along with the giant figure of the dentist, creates a sense of unease and tension.