The mystery’s opening passages describe the town of Lymstock, a fictional setting invented by Christie. A town that peaked in prosperity in the middle ages, Lymstock has retained its old-world charm but lost its connectedness and vitality. The author presents the town as quaint, but cut-off, writing that in recent centuries, “the tide of progress swept Lymstock into a backwater,” making it a “little provincial market town” (8). Nevertheless, it is a picturesque place with “placid farms and fields,” a “charming High street” and a beautiful, old church (8). The town’s appearance reinforces Joanna and Jerry’s impression that in a little town like Lymstock, “nothing nasty could happen” (7). The town’s pretty and peaceful aesthetic contrasts sharply with the darkness of the crimes and tragedies that begin to unfold, adding to the mystery of which villager could feel so vindictive toward their neighbors.

Emphasizing the village’s isolation and small, traditional population helps establish the theme of The Corrosive Nature of Social Paranoia. The accusations in the anonymous letters are only powerful because of the claustrophobic social reality of Lymstock and the mistrustful attitude the villagers have toward one another. In a city, the anonymity of a large population would render the letters almost harmless, but in Lymstock the villagers panic at the thought of their reputations being destroyed. Should their neighbors believe rumors about them, they could lose their businesses, friendships, and standing in the community. 

For instance, Dr. Griffith is upset to receive a letter accusing him of being inappropriate with his female patients, an accusation that could ruin his career and relationships if believed by others. He tells Jerry, “‘They’re all quite childish and absurd, but horribly venomous.’ His face changed, grew grave. ‘But all the same, I’m afraid. These things can be dangerous, you know’” (14). Some of the townspeople, such as Jerry and Joanna’s housekeeper Partridge, are highly impressionable, believing that “there’s no smoke without fire” (16), and thus quick to conclude that the accusations must be based on something. The atmosphere of suspicion and paranoia means that the small community, instead of offering a network of close and meaningful bonds, instead becomes a hotbed of barely suppressed hostility, as neighbors believe the worst of one another while fearing for their own reputations. 

The atmosphere of mistrust and fear also connects to the novel’s burgeoning theme on The Role of Secrecy in Small-Town Life, as the villagers do their utmost to maintain an outwardly respectable façade that does not always align with their private reality. The people of Lymstock worry about others’ impressions of them and do their best to come across as respectable and follow the village’s formal, traditional customs. Joanna is amused by their practice of leaving calling cards in their mailbox, which she is obligated to return, even though Joanna actually feels quite dismissive and even judgmental toward the villagers. The locals’ careful behavior suggests that they want to safeguard their reputation from gossip, while Joanna’s grudging socializing with them reinforces the idea that people are not behaving in authentic ways. 

The complicated relationships between the villagers provide a foundation for the story’s theme on The Consequences of Gossip and Biased Judgment. Due to her awkward demeanor, Megan Hunter is cruelly excluded by her own family as well as some of the locals. The doctor’s sister, Miss Aimee Griffith, gossips about Megan, saying to Jerry, “‘It’s not as though Megan was pretty or attractive or anything like that. Sometimes I think the girl’s half-witted. A great disappointment to her mother. The father, you know,’ she lowered her voice slightly, ‘was definitely a wrong ‘un’” (25). Megan’s mother dotes on her younger sons, but excludes Megan from their dinner party. Hurt by this mistreatment, Megan has a festering resentment toward her family and the villagers, telling Jerry, “I’ll make them all sorry. Hateful pigs! I hate everyone here in Lymstock. They all think I’m stupid and ugly. I’ll show them. I’ll show them” (56). By connecting the villagers’ poor treatment of Megan with her growing hatred of them, the author suggests that such judgment and exclusion can have serious consequences. Megan’s outburst also creates a red herring by suggesting she may be the “pathological” letter writer who is scandalizing the town, as she has a possible motive—resentment over social ostracization—to do so.