Although Mr. Nuttel's sister does not appear in the story as a traditional character, the reader hears her speak early on. To offer context for why Mr. Nuttel is paying "formal visits on a succession of total strangers," Saki includes a flashback to a conversation that took place before he left for the countryside. Despite being absent from the story's events, Mr. Nuttel's sister nonetheless pushes events of the story forward.
'I know how it will be,' his sister had said when he was preparing to migrate to this rural retreat; 'you will bury yourself down there and not speak to a living soul, and your nerves will be worse than ever from moping. I shall just give you letters of introduction to all the people I know there. Some of them, as far as I can remember, were quite nice.'
This early portion of dialogue that precedes the frame of the story shapes actions and character development. Not only does the flashback shed light on why Mr. Nuttel is sitting there waiting for the young lady's aunt at the start of the story, but it also contributes to Mr. Nuttel's character development. In the flashback, someone who knows Mr. Nuttel well—better than any of the characters the reader meets otherwise, perhaps including Mr. Nuttel himself—describes his typical behavior. Thanks to this, the reader learns early on that the character has a tendency to isolate himself and wallow in his isolation.
The flashback also develops Mr. Nuttel as someone who lets women speak over him and steer his life. While the reader assumes that Mr. Nuttel gave a response to his sister, it was evidently not forceful enough that he succeeded in turning down her letters of introduction. He clearly does not want to meet these people, perhaps he does not even want to be in the countryside, but he is nonetheless powerless against his sister's wishes. In the same way that Vera guides him through their conversation to the extent of being able to take advantage of him and mislead him, his sister has overpowered him in past conversations, presumably since they were children.
