At one point, he references the classic bawdy stories of "The Canterbury Tales" and Boccaccio's "The Decameron." That's the lineage "Nymphomaniac" aims for: a playfully told mix of sex, grief and comedy, updated for a more graphic medium. In this way, the film isn't anything particularly sensational at all.
As Joe tells it, she (played by the lithe, blank model Stacy Martin as a young woman) offered up her virginity at 15 to an Englishman named Jerome (Shia LaBeouf, with a terrible British accent), who promptly and efficiently takes it before returning to fixing his motorcycle.
She begins sleeping with countless men, cycling through as many as 10 a night. (Von Trier kindly supplies us with a series of close-ups of their genitalia.) She gathers with other girls to combat "the love-fixated society" and chant "mea maxima vulva."
She takes no apparent pleasure from the sex. "For me, nymphomania was callousness," she says. She remains unemotional even after a man, radically mistaking her signals, leaves his wife and children for her, only to be trailed to Joe's apartment by his scorned wife (Uma Thurman) and her three boys. Thurman tours the boys around the apartment to show them what their father has left them for. Thurman is exceptional in the hysterically grotesque scene.
There's a vignette of Joe's father, too, played by Christian Slater as a kind man walking through the woods with Joe, contemplating the "souls of the trees." Jerome continues to drift in and out of Joe's life, and they eventually marry and have a son.
But love has no calming effect on her lust, and she begins (in the second volume) visiting a cold, controlling S&M pro (Jamie Bell, as far away from "Billy Elliot" as humanly possible). There are other escapades, too (including a humorous one with African brothers), but it's this chapter that sets the tone of pain and self-hatred of Volume II. Naturally, this is also where Willem Dafoe comes in.