Heart of Darkness follows one man's nightmarish journey into the interior of Africa—but don't worry. No one's going to get eaten by a lion. It all takes place in the past, because what we have here is a frame story.
Aboard a British ship called the Nellie, three men listen to a dude named Marlow recount his journey into Africa as an agent for the Company, a Belgian ivory trading firm. (Mercifully, he doesn't force them to look through 1000 of his trip photos on Facebook.)
Along the way, he witnesses brutality and hate between colonizers and the native African people, becomes entangled in a power struggle within the Company, and finally learns the truth about the mysterious Kurtz, a mad agent who has become both a god and a prisoner of the "native Africans." It's more exciting than it sounds, we promise.
After "rescuing" Kurtz from the native African people, Marlow watches in horror as Kurtz succumbs to madness, disease, and finally death. In the end, Marlow decides to support Kurtz rather than his company, which is possibly morally dubious and definitely a bad career move. The novel closes with Marlow's guilt-ridden visit to Kurtz's fiancée to return the man's personal letters, and, on that ambiguous note, we end.