Here are some development sketches for the main beats of the story:
Marlow receives his assignment in France, and is soon under way to Africa.
He arrives at the first post, where he sees the depolorable conditions for the black prisoners, in comparison to the spit and polish of the white, such as the accountant.
After Marlow has repaired his steamboat, he travels upriver to retrieve the infamous Kurtz. After navigating the treacherous waters and surviving and attack by natives, they arrive at Kurtz's post, where Marlow meets a colorfully clothed Russian, who informs him of Kurtz's unorthodox methods of collecting ivory.
Finally Marlow and Kurtz come face-to-face. Kurtz, feaverish and near death, does not want to leave "his tribe," and makes an attempt to crawl back to them. Marlow intercepts him, and Kurtz is taken back down the river. He dies aboard ship.