We start with a letter—Connie's letter to Clifford informing him that she's leaving him and that she'd very much like a divorce, please.
Clifford falls into hysterics. He really shouldn't, since he's known that this was coming, but he has a fit anyway.
Mrs. Bolton tries to send for the doctor; he won't let her, but tells her to read the letter. She's not surprised, and she thinks Clifford's a little pathetic for not handling it better.
But her first responsibility is to take care of him, which she does by starting to cry—so he'll feel okay about crying. As soon as he starts, she stops and comforts him just like the little baby that he is.
After this, Clifford basically has a complete breakdown—at least at home. He and Mrs. Bolton enter into a sort of adult baby relationship, where she kisses him and he feels her up, but not in a sexual way so much as the way a child would want to be near his mom's body.
What he likes is the "exultation of perversity, of being a child when he was a man" (19.36). Mrs. Bolton thinks it's weird, but she also likes having so much power over him. And outside of the house, he's become quite the businessman. (You just know all those bankers are kinky at home.)
Finally, Clifford convinces Connie to come back to Wragby, because he refuses to do anything until she explains in person—which, honestly, she should have done in the first place. No one wants to be dumped via mail. So, she heads back, bringing Hilda along for moral support.
When Clifford and Connie are alone, she only lasts about five minutes before telling him angrily that it's not Duncan after all—well, Clifford didn't really believe it was in the first place—but Mellors.
Too bad for Clifford that he didn't just accept Duncan, because now he really flips out and says some choice things about how Connie should be "wiped off the face of the earth" (19.117). Yay, aristocracy.
He doesn't care that Connie's had an affair, but he's stunned—disgusted, really—that she would have sex with a servant. To Clifford, this proves that she's "half-insane,""not normal," and "perverted" (19.133).
For some reason—even though she's disgusting, insane, and perverted—he still refuses to divorce her. So Connie leaves to stay with Hilda in Scotland, waiting for Clifford to realize he's being a giant idiot. (It might be awhile.)
And then Connie gets a letter from Mellors, and boy is it a letter. He's learning to farm, and he likes it all right. He says some things about coal mining and how everyone depends on money all the time, and how men should learn to carve their own stools and wear little red pants—he's got a bit of thing for little red pants, evidently—and how the masses should be pagan rather than Christian.
He climaxes, so to speak, with some prophetic words about "death and destruction, for these industrial masses" (19.167), and then winds up by saying that he's actually kind of enjoying not having sex with Connie right now and that Clifford will eventually come around.
And then his penis says goodbye. And that's it for Lady Chatterley's Lover.