Miss Strangeworth did not actually see any evil. She didn't even guess that anybody in the town was doing anything evil. She sensed that there was evil behavior going on in the town, and she saw the possibilities of evil in many human relationships. The poison-pen letters she has been writing for the past year mostly hint at the possibility of evil, except for the letters she sends to Don and Helen Crane about the possibility that their adored six-month-old daughter could be mentally retarded. (The victimizing of Don and Helen Crane is a clue to Miss Strangeworth's real motivation.) According to Miss Strangeworth's twisted mind, if she hints at enough possible wrongdoings, a certain percentage will be correct. There is an element of truth to this strange hypothesis, because there is bound to be a certain amount of misbehavior going on in any community; and the bigger the community, the bigger the amount of undisclosed vice, crime, perversion, peculation, etc. If we knew all the guilty secrets of all the members of our community, all the skeletons in all the closets, we would be astonished. We do not know for sure whether Mrs. Harper's husband is having an affair with another woman. We do not know whether the grocer's grandson is stealing money out of the cash register. We do know, however, that Linda Stewart and Dave Harris, the high-school kids who love each other, are not going beyond the usual teenage necking.
Miss Strangeworth never concerned herself with facts; her letters all dealt with the more negotiable stuff of suspicion. Mr. Lewis would never have imagined for a minute that his grandson might be lifting petty cash from the store register if he had not had one of Miss Strangeworth's letters. Miss Chandler, the librarian, and Linda Stewart's parents would have gone unsuspectingly ahead with their lives, never aware of possible evil lurking nearby, if Miss Strangeworth had not sent letters opening their eyes. Miss Strangeworth would have been genuinely shocked if there had been anything between Linda Stewart and the Harris boy, but, as long as evil existed unchecked in the world, it was Miss Strangeworth's duty to keep her town alert to it.
The problem with Miss Strangeworth's method of policing the morality of "her" townspeople is that, if a certain number of guesses are correct, a much larger number must be incorrect. She is not a psychic. And she fails to appreciate the evil that exists inside herself. She tells herself she is motivated by civic responsibility, but the truth appears to be that she is full of envy and jealousy. She causes trouble for people who are reasonably happy and untroubled. A good example is Mrs. Harper. Miss Strangeworth as an old maid probably feels jealous of an old acquaintance who seems happily married. Miss Strangeworth has never had a baby, and therefore she seems sufficiently envious of Don and Helen Crane to try to poison their happiness in having a new baby. Miss Strangeworth has never known love, and therefore she could hurt inside every time she views the loving relationship between Linda Stewart and Dave Harris. Her real motives for writing her anonymous letters are evil, but they are buried deep inside her unconscious.
Actually, Miss Strangeworth is most unlikely to see much evil because she is a lonely old woman who spends most of her time in her home or in her rose garden. Agatha Christie's amateur-detective heroine Miss Jane Marple may somehow see all kinds of real evil in her little village; but Miss Strangeworth is not as intuitive as Miss Marple. When real evil comes to Miss Strangeworth in the form of having her rose bushes vandalized, she is clueless. It doesn't occur to her that Don Crane could have sent her the anonymous letter reading:
LOOK OUT AT WHAT USED TO BE YOUR ROSES