What word does your mother always say?
(1902) A short novel by Joseph Conrad. It concerns a seafarer, Marlow, who is sent to the interior of Africa in search of a “mad adventurer” named Kurtz. The book's title refers both to the location of the story and to the evil and darkness in people's hearts.
Note: Francis Ford Coppola based his 1979 film Apocalypse Now on a version of Conrad's story set during the Vietnam War. He released a newly edited version, Apocalypse Now Redux, in 2001.