Mr. Nuttel meets Mrs. Sappleton’s niece, Vera, when he first arrives at the Sappleton’s house. Mrs. Sappleton is busy and can not meet him immediately. To keep him company, Vera sits with him as he waits for Mrs. Sappleton. The story begins with Vera speaking to Mr. Nuttel:

"My aunt will be down presently, Mr. Nuttel," said a very self-possessed young lady of fifteen; "in the meantime you must try and put up with me."

In "The Open Window," how have Vera and Framton Nuttel been characterized?

Saki probably started with a germ of an idea for one of his ironic, half-funny, half-scary stories. A visitor to an English country manor is told a fabricated tale that three men died while out hunting but their crazy female relative keeps expecting them to return and leaves a French window open for them every evening around tea time. Then when the three men actually do return from hunting, the visitor believes they are ghosts and flees in terror.

But who would tell the visitor such a story? It could be the crazy wife of one of the supposedly dead men. It could be a crazy old family servant or another eccentric relative who lives on the premises. It might be a crazy neighbor who drops in unannounced, finds the visitor alone, and stays just long enough to tell him the story. And how could the visitor be so gullible? He would have to be a complete stranger, not only to the house but to the whole region.

Saki may have finally hit on the idea of making the fabricator of the "family tragedy" a teenage girl. Vera is by far the most interesting character in “The Open Window.” We understand her motive easily. She is mischievous. She is bored with her dull, confined life in this stodgy old house, and she finds her visitor unattractive and boring. She doesn’t like being stuck with him while her aunt is getting ready to come downstairs. She knows she is being given a practical lesson in playing a hostess, but she doesn’t want to grow up to be just like her aunt, a brainless woman with an endless repertory of small-talk.

The idea of using a teenage girl for this role was especially appealing because she serves as such a sharp contrast to the other character, Framton Nuttel. She is young. He is middle-aged. She is female. He is male. She is healthy and full of energy. He is a hypochondriac. She is described as “self-possessed.” He is ill at ease because he is naturally shy and nervous and doesn’t like imposing on perfect strangers with nothing but a letter of introduction. We can picture Vera  wearing a long, rather shapeless dress in the style of the period. We picture Nuttel wearing a tweed suit with a vest and a necktie. It is easy for an author to describe characters and write their dialogue when they are so different in so many respects.

In "The Open Window," how have Vera and Framton Nuttel been characterized?

In "The Open Window," Framton Nuttel is characterized as the nervous type. He has taken some time away from things to calm his nerves. He visits the Sappletons in hopes of having a nice, relaxing time. While waiting for Mrs. Sappleton to come down, Nuttel meets Vera. Vera is a fifteen-year-old girl with a mischevious streak. 

Obviously, Vera recognizes that Nuttel is the nervous type and she decides to have some fun with him. She begins a tall tale about why Mrs. Sappleton has left the window opened. She mentions that three years ago Mr. Sappleton and his brothers-in-law walked out through the open window to go hunting. Since then, they have not returned. 

Now, Mrs. Sappleton is in mourning for her husband. She refuses to close the window in hopes that they will return one day.

Nuttel becomes more anxious as Vera tells her tall tale. Finally, Mrs. Sappleton comes down to meet Nuttel. She has no idea about the tall tale that Vera has shared with Nuttel. Mrs. Sappleton talks of her husband as if he had just gone hunting that morning, which is exactly what had happened. Vera has used her imagination to try and frighten Nuttel. 

When Mrs Sappleton sees her husband and brothers, she declares, "Here they are at last!" With this comment, Framton Nuttel is frightened out of his wits and he runs out of the house without saying goodbye. Thanks to Vera, Nuttel leaves with his nerves worse than ever. 

Of course, the author agrees that Vera's specialty is making up tales:

As Saki remarks at story's end, making up stories that add a bit of excitement to life, ''romance at short notice," is Vera's specialty.