First things first: we're going to go chronologically here, even though the book jumps around a ton. Just FYI.
Sethe grows up on a plantation, raised and nursed by a woman who isn't her mother because her mother is always working in the fields.
At the age of fourteen, Sethe is sold to the Garners and moves to Sweet Home.
The Garners give her the freedom to be with Halle, although they can't legally get married. Mrs. Garner gives Sethe crystal earrings to honor her "union."
Sethe has four children with Halle: Howard, Buglar, a baby girl, and Denver.
She's pregnant with Denver when Mr. Garner dies and schoolteacher comes to Sweet Home.
Sethe agrees to escape Sweet Home with Halle and the other slaves, but their plan fails.
Sethe manages to get her sons and her baby girl onto the fugitive slave train, but she stays behind to find Halle.
That's when schoolteacher finds and beats her. Then he lets his two boys rape her.
Traumatized, Sethe runs away and makes it to the Ohio River, where a white girl named Amy Denver gets her to safety.
Stamp Paid delivers Sethe across the river and helps reunite her with her kids at Baby Suggs's. They're all happy for a few months.
The day Baby Suggs throws a huge party, schoolteacher comes with his two boys and a slave-catcher for Sethe and her kids.
Cornered, Sethe takes her children into the shed and kills her baby girl. She tries to kill Denver too, but Stamp Paid stops her.
After that, schoolteacher doesn't want her anymore, so Sethe's sent to prison.
When she gets out, she returns to 124 as the town pariah and eventually takes over the house once Baby Suggs dies.
About 18 years later, Paul D arrives at 124. He and Sethe promptly have sex and start a relationship.
Not long after, Beloved shows up on the porch, and Sethe takes her in. Sethe is over the moon about Beloved despite Paul D's disapproval.
She and Paul D end up fighting about Sethe's murderous past, so Paul D moves out.
Beloved becomes her whole world instead. Sethe quits her job and spends all her time keeping Beloved happy, even though Beloved becomes more demanding and Sethe eventually has nothing left to give.
The day the women in the town arrive to exorcise Beloved, Sethe sees Mr. Bodwin coming down the road and mistakes him for schoolteacher. She tries to kill him, but the women stop her. During the fracas, Beloved disappears completely.
Sethe's lost without Beloved until Paul D returns to take care of her and convince her that they can build a new life together.