There are several examples of frame stories throughout Dr. Jekyll and Mr. Hyde, as key revelations and scenes in the narrative are told through correspondence, conversation, sealed messages, and secret documents. The last chapter in particular (“Henry Jekyll’s Full Statement of the Case”) explains Jekyll’s experiments with Hyde, as well as the events of the novel, from Jekyll’s perspective.
Henry’s motivation for writing a fuller explanation of his situation, unflattering and fantastic as it is, is difficult to assess. Perhaps he, correctly, believes no one else could possibly fully explain the war between the two halves of his interiority. This is surely Stevenson’s motivation for including it. This letter, like the other secondary accounts in the story (the letter from Lanyon, Poole’s account of Jekyll’s behavior, Enfield’s account of the door, the maid’s witness to Carew’s murder), allows Stevenson to explore a subjectivity beyond Utterson’s. While the narrative is written in the third person, it follows Utterson’s thoughts and actions closely and is limited by his perceptions. The frame story of the letter therefore allows the reader to dive deeply into Jekyll’s perception of the same actions and events, ultimately enabling the reader to judge Jekyll’s character and intentions without any outside point of view clouding the account.