Heart of Darkness is best known as the story of Marlow's journey to Africa, which, in part, it is. However, the novel is also the story of a man on board a London ship who listens to Marlow's story as well. This "story-within-a-story" form is called a frame tale. (The significance of the framing device is discussed in the Critical Essays section.)
Exploring man's inhumanity toward other men and raising some troubling questions about the impulse toward imperialism, Heart of Darkness is also an adventure story where (such as many others) the young hero embarks on a journey, and in the process, learns about himself. Marlow begins his narrative as a rough-and-ready young man searching for adventure. Unlike those of Europe, the maps of Africa still contained some "blank spaces" that Marlow yearned to explore; his likening the Congo River to a snake suggests the mesmeric powers of Africa. However, the serpent is also a well-known symbol of evil and temptation, harkening back to the Book of Genesis in the Old Testament. Thus, Conrad's comparing the river to a snake also suggests the danger Marlow will find in Africa and the temptations to which Kurtz succumbs when he sets himself up as a god to the natives. Despite the uncertainty of what lay there, Marlow had to go.
However, before Marlow even sets foot on the African shore, Conrad begins to alert the reader to the terrible power of the African jungle. Marlow learns that a piloting position has become open because a chief's son has killed one of the Company's pilots over two black hens. Fresleven, the dead pilot, was thought by all to be "the kindliest, gentlest creature that ever walked on two legs," but Conrad hints that something caused him to shed his self-control (as a snake sheds its skin) and attack the chief of a village. (This something, being the effects of "the jungle" on uninitiated Europeans, becomes more and more pronounced to Marlow and the reader as the novel progresses.) Marlow eventually sees Fresleven's remains on the ground with grass growing up through the bones. The image suggests that Africa itself has won a battle against Fresleven and all he represents. The earth reclaimed him as its own, and Nature has triumphed over civilization. This is the first lesson Marlow learns about the futility of the Company's agents' attempts to remain "civilized" in the jungle, which releases instinctual and primitive drives within them that they did not ever think they possessed.
