Marlow frames his story aboard the Nellie. He describes getting the job in Brussels, then traveling to the Outer and Central Stations. In the first station, he sees laboring black Africans for the first time, and is appalled at the inhumane conditions under which they work. Here, he first hears the name of Kurtz and slowly becomes more and more intrigued as he keeps hearing news about the remarkable agent. When he reaches the Central Station, he finds the steamboat intended to take him into the interior has had an accident and will require three months to repair. Here, he meets the manager, the brickmaker, and manager’s uncle – the head of the Eldorado Exploring Expedition. In true Marlow fashion, he doesn’t like any of them.
Marlow learns more about Kurtz by eavesdropping on the manager and his uncle. He learns that they – like the brickmaker – have hopes of getting promoted and Kurtz’s stunning outputs of ivory threaten their ambition. Marlow becomes fascinated by Kurtz. His journey from the Central Station to the interior is nightmarish. When he and his crew near the Inner Station, they are inexplicably attacked by a group of Africans. They survive with only one casualty, but the pilgrims are shaken. However, Marlow is determined to go on. They discover a little hut where Marlow finds a seaman’s book, something he takes great comfort in. When they arrive at the Inner Station, Marlow meets a curious man dubbed the harlequin who apparently knows Kurtz.
Marlow befriends the harlequin, who tells him all about Kurtz. Kurtz has allied himself with the native Africans and uses them to raid other villages and steal ivory. The Africans see him as a god among men and worship him. Marlow learns that Kurtz ordered them to attack his steamboat because he does not want to be taken away from the interior and his precious ivory stash. At this point, we see Kurtz for the first time – sick and brought in on a stretcher by his Africans. The manager has a private interview with him to make arrangements to take him back to Europe. The harlequin decides to make a run for it. Later that night, Marlow wakes up to find Kurtz gone. He discovers him crawling off in the woods and decides to take him back. The next morning, the Africans cause a great disturbance as Kurtz is loaded onto the steamboat. On the return trip, Kurtz dies horribly in the grip of his hallucinations. Once back in England, Marlow finds himself ostracized by his crew and unable to return to a normal life. So he concerns himself instead with returning Kurtz’s letters to his fiancée. His visit to her proves that everyone thinks the world of Kurtz, despite his depravity. Kurtz's Intended thinks that the last words Kurtz said were her name and Marlow allows her to think this when Kurtz’s true last words were the much darker, "The horror! The horror!"