In the following passage from the fourth letter, Lady Susan discusses her sister-in-law, Catherine Vernon, with Mrs. Johnson. Lady Susan's status as an unreliable narrator and manipulator feed into and contribute to verbal irony, generating a passage that perhaps serves to obscure a more accurate view of events:
I wanted her to be delighted at seeing me—I was as amiable as possible on the occasion—but all in vain—she does not like me. To be sure, when we consider that I did take some pains to prevent my Brother-in-law’s marrying her, this want of cordiality is not very surprising—and yet it shews an illiberal and vindictive spirit to resent a project which influenced me six years ago, and which never succeeded at last.
Lady Susan claims that she did all that she could to please her sister-in-law; however, since she has been established as an unreliable narrator, her words likely contradict her actions. She states that she wants her sister-in-law to like her; and, indeed, Lady Susan also claims to like her sister-in-law, but the reader cannot take this claim at face value. On the opposing side, Mrs. Vernon cannot be entirely absolved of blame: she clearly has a certain level of bias against Lady Susan. No matter how merited that bias may be, it still prevents Mrs. Vernon from being an objective narrator.
Though all of the characters in Lady Susan are arguably unreliable narrators, Lady Susan, the titular character, provides the most obvious and extreme example thereof. The first letter that appears in the novel is written by her, and, all things considered, appears fairly innocuous at first glance. She states at the beginning of the first letter that
[...]if quite convenient to you and Mrs. Vernon to receive me at present, I shall hope within a few days to be introduced to a Sister, whom I have so long desired to be acquainted with.
At first, this statement is pretty harmless, and the reader is primed to take it at face value. After reading the other characters' accounts of Lady Susan, however—in particular Mrs. Vernon's—the reader comes to understand that Lady Susan is not at all excited to meet her sister-in-law, but in fact quite despises her.
Crucially, this limited, unreliable perspective is the only type of perspective that the first-person, epistolary format of Lady Susan permits readers to engage with. Without an omniscient narrator, all characters become unreliable narrators of their own stories, forcing the reader to consider and decide for themselves what constitutes an accurate version of events.
In Letter 17, written to Lady De Courcey, Mrs. Vernon discusses Lady Susan's behavior upon the arrival of Frederica at Churchill. This passage begins to establish Mrs. Vernon as an unreliable narrator of events:
This pathetic representation lasted the whole evening, and so ostentatious and artful a display has entirely convinced me that she did in fact feel nothing.— I am more angry with her than ever since I have seen her daughter.— The poor girl looks so unhappy that my heart aches for her.
While the reader has undoubtedly grown used to considering Lady Susan the central unreliable figure, the content of this passage, along with that which precedes it, would suggest otherwise. Lady Susan is clearly an unreliable narrator, but Mrs. Vernon is no less one herself: in this passage, she assumes many things about Lady Susan's behavior towards Frederica. Clearly, Mrs. Vernon is biased against her sister-in-law and predisposed to think ill of her. While these prejudices are not entirely unfounded, they may lead to an overstatement of the situation as Mrs. Vernon conveys it to her mother. Frederica may be unhappy; but that unhappiness may not be as extreme as Mrs. Vernon believes it to be. One cannot know this without later hearing Frederica's perspective.
