According to the niece, Vera, the aunt leaves this window open, awaiting the return of her husband and brothers. No matter how cool it may be, this window is open. Since the husband and brothers disappeared through this window, it makes sense for it to be open. It makes sense that the aunt has lost her reasoning skills from the heartache of losing her husband and brothers. Since she last saw them leaving through the open window, it makes sense that she would desire to keep the window open as she waits for her husband's and brothers' return.
Although the complete story the niece tells is a tall tale, the reader does not know the truth and neither does the gentleman, Mr. Nettel, who is calling upon the aunt:
Exactly three years ago, Vera recounts, Mrs. Sappleton's husband and two younger brothers walked through the window to go on a day's hunt. They never came back. They were drowned in a bog, and their bodies were never found. Mrs. Sappleton thinks they will come back some day, along with their spaniel, so she keeps the window open.
Vera, the niece, is quick witted and amazingly talented. She uses the open window as part of her far-fetched story. It just so happend that the window was open for the husband and two brothers. Vera is quick in her thinking. She creates a tall tale based on the open window. The husband and two brothers did walk through the open window to go hunting. They are now coming home and will once again walk in through the open window. It makes sense to create a tale about the open window for the husband and two brothers are expected to return at any moment.
No doubt, Mr. Nuttel was wondering why the window would be open. Mrs. Sappleton gives an apology and explanation for the open window:
Mrs. Sappleton excuses the open window, explaining that her husband and brothers will be home soon, and she continues to talk on quite cheerfully about shooting.
Vera knew the aunt would make such an apology, thus corroborating her tall tale. Vera is clever. She knew the aunt would go on and on about the open window, even to the point of apology for it being open. This in turn set Mr. Nuttel up for the tall tale. Most people do not keep their window (door) open. Mr. Nuttel finds himself feeling sorry for Mrs. Sappleton until he actually sees the husband and two brothers returning. He finds his way out the other door, desiring to be no part of the welcoming committee:
It is no surprise that Mrs. Sappleton' s niece tells a story that is easy to believe. She begins with an object in plain view, an open window, and proceeds from there. The window is obviously open, but for the reasons for its being open the reader is completely at the mercy of Mrs. Sappleton's niece, at least while she tells her story. The open window becomes a symbol within this story-within-a-story, and its appearance becomes its reality.