The mood of "The Open Window" goes through multiple shifts. When the story opens, the mood is stiff and awkward. As the self-possessed Vera tries to get to know Mr. Nuttel—and scope out the prospects for tricking him—the awkwardness of their interaction feels comical. When Vera takes over the narrative with her tragic tall tale, however, the mood turns uneasy. The stiff yet light mood of the exposition quickly becomes effaced by the diction of words like "great tragedy," "engulfed," "treacherous," and "dreadful." The uneasy mood takes on a scary quality just before Mrs. Sappleton arrives:
'Do you know, sometimes on still, quiet evenings like this, I almost get a creepy feeling that they will all walk in through that window-'
She broke off with a little shudder.
This scary quality remains throughout the interaction between Mr. Nuttel and Mrs. Sappleton and then becomes heightened when the men actually arrive at the house.
Framton shivered slightly and turned towards the niece with a look intended to convey sympathetic comprehension. The child was staring out through the open window with dazed horror in her eyes. [...] In the deepening twilight three figures were walking across the lawn towards the window.
After the climax, however, as Mr. Nuttel flees and the truth is revealed, the mood returns to being light and comical. This final shift of the mood is punctuated by the last sentence, which empties the story of all the prior tension and uneasiness: "Romance at short notice was her specialty."
