Jack Durbeyfield learns from the local parson that he's actually descended from the ancient, noble family of the D'Urbervilles. But what good is an ancient family when you're barely scraping by? Jack Durbeyfield doesn't pause to reflect on that, but instead gets all puffed up with pride at the thought of his ancestors being knights and wealthy noblemen. He starts living in the past, instead of dealing with the present and planning rationally for the future.
Jack Durbeyfield is only willing to plan for the future insofar as it allows him to glorify his family's past. So he sends Tess, his oldest and most educated child, to borrow money from their distant relations. It turns out, of course, that the family called "D'Urberville" in the next town over just added that name to their own because it sounded noble and they thought that all the real D'Urbervilles had died out – they're not related to the Durbeyfields at all. Alec D'Urberville, the son of that family, is totally smitten with Tess. He tries to seduce her, and fails. So he takes advantage of her dependence on him to get her by herself in the forest, and rapes her.
Tess is no longer a virgin, which means she's not exactly marriageable anymore, according to 19th century English principles. She leaves home for a fresh start and, despite her resolution never to marry, she falls in love with Angel Clare, a gentleman's son who's learning about dairy farming. How will she resolve her decision never to marry with her desire to be with Angel?
Of course love triumphs over everything else, and Angel finally persuades Tess to marry him. He doesn't know anything about her history, and she keeps trying to tell him, but isn't able to. She even writes it all down in a letter to him, but he never receives it. So on their wedding night, she confesses everything.
Angel can't believe that Tess isn't the pure and unsullied country girl that he thought she was. His whole worldview collapses when she confesses that she's had sex (even though it was a rape). So he leaves her with money, and instructions on how to get more from his family if she needs it. But Tess is too proud to ask for help, and ends up working as a farm laborer to make ends meet while Angel's gone. While Tess is living on her own, Alec sees her again for the first time since the rape. He becomes obsessed with her again, and stalks her and harasses her until she finally tells him that she's married to someone else.
After much harassment and taunting, Alec persuades Tess that Angel will never come back again. Her father dies, and her mother and younger sisters are going to be left out in the cold. Alec offers to give them a house and schooling…if Tess agrees to marry him.
course, Angel does come back. He realized just how wrong he was, and comes back to find Tess and beg forgiveness. But it's too late! She's already married Alec, and when she sees that Angel has come back for her, and still loves her, she murders Alec. She and Angel flee together to avoid the authorities, and she's finally arrested, tried, and executed