The plot follows the slave Margaret Garner as a new master comes to Maplewood, the Kentucky plantation she works on. Margaret catches her new owner's eye and is brought in to work in the "big house" and her husband, Robert, is rented out to another farm. While the widowed plantation owner, Edward Gaines, sees Margaret as a sexual object, his daughter, Caroline, comes to see Margaret as a sort of foster mother. At Caroline's engagement party, a rift develops between Edward and his daughter over her respect for Margaret. Robert returns to escape with Margaret and his children; his mother Cilla refuses to go, claiming to be too old to learn the new habits of freedom. While they prepare to escape, the overseer, Casey, finds them and, after a struggle, Robert kills him. The couple and their two children flee, but are later found by Edward and a posse. After a gun fight, Robert is captured and lynched. Margaret kills her two children to prevent them being returned to slavery but she is taken alive. Edward forces a criminal trial where Margaret is charged with "destruction of property" for the killing of his slaves, her children. Caroline appeals to Edward to advance the abolitionist agenda by having Margaret tried for murder instead, acknowledging the slaves' humanity. Edward refuses, but after the verdict and sentence of execution, fearing losing Caroline but still believing he acted as a "proper" gentleman, he obtains a commutation for Margaret if she admits her guilt. Ignoring him, Margaret herself steps off the gallows.
Historical Accuracy
The opera does not intend to be accurate history. Some of the differences between the story of the opera and actual events are:
Robert Garner did not kill anyone, and was not lynched. In a shootout, he wounded two of the slave-hunters sent to recapture his family. He survived the escape and recapture, and fought on the Union side in the Civil War. He raised two sons, Tom and Sam, and died in 1871 from a chest injury suffered while working on a ship.
Margaret Garner was pregnant at the time of her escape, and killed only one of her children, Mary, when faced with recapture; of the three other children, two sons, Tom and Sam, lived to maturity; a daughter Cilla was drowned at the age of ten months when she and Margaret were thrown overboard in a collision of their steamboat (headed for the slave market in New Orleans) with another ship. Margaret was not hanged, and survived the collision. She was remanded with the remaining members of her family to their Kentucky slaveholders, and then sold to a plantation in Mississippi, where Margaret died of typhoid fever in 1858.
Margaret's trial was focused primarily on the Fugitive Slave Law of 1850, rather than on the killing of her daughter.