Write to The Possibility of Evil where Miss Strangeworth is faced with endless torment from her neighbor.

In the story, Miss Strangeworth believes that she is doing a public service by sending anonymous letters of "concern" to her fellow townsfolk. Each of the letters are, however, filled with innuendo, wild speculations, and vindictive allegations.
We are told that Miss Strangeworth writes her letters on pink, blue, yellow, and green paper. She uses matching colors for her envelopes as well. In the story, she chooses pink paper for her note to Don Crane. In her letter, Miss Strangeworth cruelly insinuates that Don and his wife, Helen, have a developmentally delayed child on their hands.
Miss Strangeworth also writes to Mrs. Harper. She uses green paper and presents a callous truth to her neighbor without embellishment:

HAVE YOU FOUND OUT YET WHAT THEY WERE ALL LAUGHING ABOUT AFTER YOU LEFT THE BRIDGE CLUB ON THURSDAY? OR IS THE WIFE REALLY ALWAYS THE LAST ONE TO KNOW?

Miss Strangeworth writes one more letter, a blue one to Mrs. Foster. The text tells us that she puts all three letters (pink, green, and blue) into the post office box slot. However, a letter falls out. Miss Strangeworth does not notice this, but a boy (surnamed Harris) and his girlfriend, Linda, do.
The teenagers deliver the letter to Don Crane themselves after reading the name on the pink envelope. The story ends with Miss Strangeworth receiving a delivery of letters to her home. One of the letters is written on green paper, and it reads,

LOOK OUT AT WHAT USED TO BE YOUR ROSES.

From the story, we learn that Miss Strangeworth used green paper for Mrs. Harper's note. By all appearances, Mrs. Harper is well aware of Miss Strangeworth's habit of writing cruel notes to anyone she pleases. Note, however, that the author does not reveal how Mrs. Harper discovered Miss Strangeworth's authorship of the letters.
The text suggests that Miss Strangeworth herself is oblivious as to how her new tormentor could have ferreted out her identity. The ambiguous threat against Miss Strangeworth's roses suggests that the "possibility of evil" will soon cloud the old lady's present and future happiness. Miss Strangeworth's new tormentor appears to be the only one who knows about her letter-writing habits, and there is every indication that the tormentor will use it to her advantage. We can only speculate that the identity of the likely tormentor is Mrs. Harper.
So, the tables have been turned. In the past, Miss Strangeworth introduced ambiguous fears into other people's lives on a regular basis. Now, she will be the one living in fear. It appears that the "possibility of evil" will haunt Miss Strangeworth's days, as she will have little idea of when her tormentor will strike.