Connie and Clifford are married. They have a nice house—an estate, really; a not-so-nice coal mine; and a couple of big problems.
They get by all right for a while. Clifford writes some really modernist, depressing stories and people like them. Modern young men and women come visit and have intellectual conversations about how bad everything is, particularly sex and love. One of these modern young men, a really vulgar Irish playwright named Michaelis, convinces Connie to have sex with him. For a while, it's awesome. She feels much better about everything, even if he kind of jumps the gun every time they get in bed together. He even tries to convince her to marry him. When she hesitates, he says some nasty things about modern women and totally harshes Connie's mellow.
Now things really start to go south for Connie. She's getting fed up with an increasingly needy and dependent Clifford, so she and her sister, Hilda, convince him to hire a nurse, Ivy Bolton. Ivy is incredibly vulgar, but Clifford likes her anyway—who wouldn't like someone catering to his every whim?
Around this time, Connie starts hanging out in a hut on the edge of the clearing where the gamekeeper Oliver Mellors is raising some pheasant chicks (the bird kind) to stock Wragby park. They instantly hate each other, so of course they end up having wild, passionate sex and then endlessly talking about how great their sex is, like that really annoying couple you have to stop hanging out with for about six months after they start dating.
Mellors has a lot to say. He's from a coal-mining family, but he bettered himself through literature (natch) and then got fed up with modern men and women (sensing a theme here?) and decided to go back to working with his hands. He says some nasty things about pretty much everyone, and Connie eats it up with a spoon.
Eventually Connie finds herself pregnant. Clifford has actually told her he'd be okay with raising another man's child so long as Wragby gets an heir, but by now she can't stand to be around Clifford. She goes to Venice with her sister and father with the intention of faking an affair with a more appropriate guy—gamekeepers are a little déclassé—and they convince her to get a friend of the family to help her file for divorce.
Back at the ranch, Mellors's estranged wife has shown up to be all nasty, the Miss Jackson kind, to him and accuse Lady Chatterley of being his lover. Clifford doesn't exactly believe it, but he fires Mellors just in case. Connie heads home, confesses, and asks for a divorce. Clifford, for some insane reason, refuses. When the novel ends, everyone's waiting: Mellors is learning how to farm and waiting for his divorce to go through; Connie is waiting for the baby to be born so she can leave Wragby; and they're both waiting for Clifford to realize he's being a giant jerk and give Connie the divorce.