at the end which is kept hidden by the narration.
Told from a third-person omniscient point of view, the reader learns about the town and the main character, Miss Adela Strangeworth, through this unlimited perspective, but just because the narrator knows everything about her doesn't mean they relay everything they know. It's almost as if the narrator intentionally frames the narrative in favor of Adela which deceives the reader.
Another notable device is the positive diction used which creates vivid imagery for the reader. While the story title connects to the concept of evil, the setting seems pleasant, along with the characters.
For example, look at the opening passage:
Miss Adela Strangeworth stepped daintily along Main Street on her way to the grocery. The sun was shining, the air was fresh and clear after the night’s heavy rain, and everything in Miss Strangeworth’s little town looked washed and bright.
Positive diction such as "daintily," "fresh," and "bright" make the scene feel beautiful and ideal.
We see this cheerful imagery again when Miss Strangeworth approaches her home:
From halfway down the block Miss Strangeworth could catch heavy accent of her roses, and she moved a little more quickly. The perfume of roses meant home, and home meant the Strangeworth House on Pleasant Street.
The positive diction and vivid imagery create a cheery and unassuming tone which begins to shift once Adela starts writing her letters. It's these letters that become a cause of concern for the reader, leaving them to wonder who this woman is and why she is so critical. The mood shifts from pleasant to confused to downright dark.
In the end, we see the ultimate irony. Miss Strangeworth accidentally drops the nasty letter she was going to send. The Harris boy, thinking he is doing a kindness for Adela, picks up the dropped letter and brings it to the recipient. However, this moment of dramatic irony reveals the truth to the town about the evil that has silently been brewing.
We also find irony in Adela's letters. She believes she is doing the right thing by ridding the town of the "evil" the townsfolk create, yet Adela is the one spreading said hate by insulting each and every person living there.