Don't let the dense verbal foliage fool you: deep under the thorny entanglements of Conrad's prose, his second language (!) facilitated here better than native writers, there lies a deep dark truth about human nature that chills the soul with horror.
Marlow is our narrator. He reveals that (at the height of imperialism) he is being sent as an emissary from a Belgian company to determine what happened to his predecessor Kurtz, a highly respected and accomplished officer who has either gone missing or purposely disappeared in the depths of the Congo in the middle of Africa. Through four sections of this novella, Marlow literally enters into the heart of the African continent, passing a couple of outposts where he receives disconcerting news about the possibilities of Kurtz, and a few hostile "welcomes" along the way. One of the highlights of literature is the climax of the story, when he finally encounters Kurtz and learns the truth of his expedition and the establishment of his own "colony".
A highlight of modernism, Conrad's story is a belwether for the concerns of the twentieth century. Written 15 years before the outbreak of World War I, it somehow anticipates several of the causations of that massive conflagration. Kurtz is one of the great characters in Modernism (notice his ambiguously international name), and when he begins to speak, we like Marlow can't help but listen. If Marlow represents us, then his blind spots are ours as well; racial stereotyping is present as is that naive innocence of the consequences of a "righteous cause" emblematized by the flag of our nation or our company. Is that "heart of darkness" deep within the Congo, or is it merely a reflection of the darkness within our own souls?
Conrad's classic continues to be required reading, but don't let that or the dense prose style fool you. Conrad was one of the first to turn his imperialist gaze outside his own boundaries (perhaps because of his status as an outsider within the British culture as a Polish immigrant) and to see the darker side of self righteous expansionism and profiteering disguised as some kind of missionary work to spread enlightenment through commercial enterprise. In the end, we are only left with the horror of the consequences of our deeds and the horrific truth that we have become distorted from our original intents - if they were even truly pure to begin with and not self deception all along.
An essential in all of literature. Chills at midnight type stuff.