Suffice to say that essentially the book is in four parts: the protagonist's experience of war, Africa, America, and then his experiences (partly as a qualified doctor) back in France. Throughout the book, which is only loosely autobiographical, Ferninand Bardamu has brief flings with various women, and keeps meeting Léon Robinson (who appears to have some kind of relationship to Bardamu's self), who is killed very near the end by Madelon, Robinson's jealous lover, who's shortly before suggested (anonymously) that Robinson and Bardamu are in a gay relationship, and even says that they're in a threesome with Bardamu's current lover Sophie.
But all this has been written about many times before, and the essential is that Voyage au bout de la nuit is a fierce criticism of war, of the violent and racist colonial system, and of the extremes of capitalist society witnessed in New York and Detroit. More importantly, though, it's the way these criticisms are made, because the novel introduces popular speech not only into the quotations of its characters (very frequent slang and 'taboo' words, the negative 'ne' missed as in ordinary spoken French, ellision as in 'T'as raison', etc), but this kind of language is also used by the narrator himself. Céline's writings had a great influence on a great number of people, and he is considered by many critics to be, along with Proust, one of the two greatest writers in French in the last century.
There. And I didn't even mention anything about pamphlets.