The problem in "The Open Window" is that one shaken psychological force, in need of a "nerve cure," meets an imaginative psychological force with an art for "[r]omance at short notice," then explosive psychological manipulation occurs. In a sense, you might say there is no resolution to the problem because the central character affected by the problem, Framton Nuttel, finds neither peace nor harmony following the climax (seeing three figures out the window) and falling action (specifically, running speedily away).
Framton grabbed wildly at his stick and hat; the hall door, the gravel drive, and the front gate were dimly noted stages in his headlong retreat. A cyclist coming along the road had to run into the hedge to avoid imminent collision.
However, there is a resolution to the problem of the story that directly involves readers and Vera. When Framton runs "in his headlong retreat," the reader is left at the house with Mrs. Sappleton, Vera, and the three figures with the spaniel. We find out, though Framton does not, that these figures are real men, not figures of long lost ghosts. We also find out the truth of the joke played on Framton and on us (wish Framton could have stuck around a bit longer). Vera is woefully given to telling tall tales on a whim, using any information or circumstance that comes her way. So the actual resolution here has to do with Vera rather than poor Framton, who is much the worse for wear, I fear, for having met Vera.
Vera was telling a complete fiction based on the family's daily habits. Vera's aunt and uncle have not the slightest idea of Vera's tale-telling past-time. Vera will continue to tell tales to everyone's disadvantage but her own--and--she will continue to feel no remorse.
"[He] dashed off without a word of goodby or apology when you arrived. One would think he had seen a ghost."
"I expect it was the spaniel," said the niece calmly; "he told me he had a horror of dogs. He was once hunted into a cemetery somewhere on the banks of the Ganges by a pack of pariah dogs, and had to spend the night in a newly dug grave ... just above him. ...."