Conrad wrote Heart of Darkness as a first-person narrative. Marlow, the protagonist, tells his own story from his own perspective. Thus, the reader experiences the story from Marlow’s point of view. Owing to the subjective nature of first-person narration, a certain degree of unreliability is unavoidable, and Marlow’s narration is no different. That said, what makes Marlow’s narrative unreliable is not solely that he speaks from his own subjective point of view, thus making it easy for the reader to be suspicious of what he says or what his motivations for speaking are. Indeed, Marlow does not populate his story with exaggerated tales or highly improbable occurrences, nor does he skimp on details. For this reason, Marlow is not unreliable due to a suspicion that he is misreporting or underreporting. Instead, he is unreliable due to his inability to make sense of his experience. Marlow frequently emphasizes the difficulty he has interpreting his own story, and his doubt causes the reader to be skeptical about Marlow’s capacity as a narrator in the first place. If he is not fully in control of his story and the meaning it contains, why, the reader wonders, is he telling it at all? 

Because Heart of Darkness makes use of a frame narrative, there is a second narrator. This second narrator also speaks in the first person, and in his narrative, the reader sees Marlow from an outside perspective. This narrator is skeptical of Marlow, and he uses irony to indicate this. For example, when Marlow begins his story with the dramatic claim that England is “one of the dark places of the earth,” the frame narrator explains that this sense of drama is characteristic of the man and that his comment is “accepted in silence,” suggesting that the other passengers are also familiar with Marlow’s storytelling. Although the vast majority of the novella is told from Marlow’s perspective, the frame narrator interrupts the story at several points, usually at moments when Marlow falls silent. At these moments, the frame narrative reorients the reader’s perspective, serving as a reminder to step back from Marlow’s story and evaluate it. These interruptions also provide the reader with a sense of the passage of time. The novella opens near dusk, and by the time Marlow goes silent for the first time (just before the end of part I), it is already dark.