Miss Strangeworth makes the mistake of thinking that her nasty little campaign of poison-pen letter-writing will have no consequences. She acts like she owns the town; she is its self-appointed moral guardian. This is largely due to her grandfather's being the first man to build a house on Pleasant Street. Miss Strangeworth thinks that this gives her a privileged position from which she can tell other people how to live their lives. This is her town, and these are her people. So arrogant is she that she doesn't stop to think for one moment that, one day, her unpleasant actions might come back to haunt her.
And that's precisely what does happen, but entirely by accident. One evening, Miss Strangeworth is posting three more of her poison-pen letters. But unbeknownst to her, one of them falls to the ground. Someone must pick it up and then realize who's been sending all these horrible letters. The nasty letter she subsequently receives is payback for all the ones she's sent herself. Now that Miss Strangeworth has been exposed to the whole town as a thoroughly unpleasant piece of work, her reputation, like her prize rosebush, has been destroyed.