The following version of the book was used to create this study guide: Kelly, Martha Hall. Sunflower Sisters. Penguin Random House, New York, NY, 2021. Kindle AZW file.

Georgy Woolsey is one of seven sisters of the Woolsey family, led by the matriarch Mrs. Charles Woolsey. Strong and independent, Georgy is among the first to volunteer as a nurse when the Civil War breaks out. Over the first year of the war, she finishes her training and works alongside her sister, Eliza. The family are staunch abolitionists, and Georgy's sisters support the Union through various efforts, including gathering and distributing donations for the troops.

While Georgy's family is working for the cause, Jemma is one of the slaves on the Peeler Plantation, growing tobacco. Her previous owner taught several of the slaves to read, only so they could read to her. The new mistress of the plantation is Anne-May Wilson Watson and her husband, Fergus. Fergus is kind to the slaves, but Anne-May is often cruel and demanding. Anne-May allows Jemma to write because she does not want to write. Jemma is in charge of recording the new slaves that arrive on the plantation, including two girls – Celeste and Delly. Jemma soon becomes friends with Celeste and shows her a book from Anne-May's library, Uncle Tom's Cabin. She helps Celeste begin learning to write by writing her name in the book. LeBaron, the cruel overseer, kills Celeste and later hangs Jemma's father, Joseph. Anne-May's brother fights for the Confederacy and dies in the war while Fergus loses a leg fighting for the Union. Anne-May's bitterness grows. With the help of a merchant named Jubal Smalls, she begins passing information about Union movements, aiding the Confederate Army.

Anne-May's world begins to fall apart when Jemma leaves the plantation without revealing the location of a book filled with the information Anne-May and Jubal passed to the Confederacy. Jemma ends up at Gettysburg where she is wounded and meets Georgy and Mrs. Woolsey, who are serving as nurses. Jemma travels to New York with the women. When Anne-May faces charges of being a spy, she gives up some information in return for her freedom and manages to return to the plantation with Jemma. Jemma discovers that LeBaron has bought her twin sister Patience. The girls kill LeBaron in their determination to escape. Anne-May discovers her husband and sister Euphemia are having an affair and that Jubal is planning to hand her over to officials to save himself. In a showdown near the plantation, Anne-May kills Jubal. Officials make posthumous charges against Jubal and against Anne-May as his accomplice. While in jail, she sees that LeBaron's men have burned the plantation house. When she is released, Anne-May sleeps in the slave shack, comforted only by her cat. With the war winding down, Georgy finally faces her love for a doctor named Frank Bacon, and they marry. The day is bittersweet because Georgy's sister Mary pushed Frank to propose again but died before the wedding.

Meanwhile, Jemma and Patience make their way to Bethlehem, Connecticut, where they reunite with their mother Sable and a dear friend named Delly. They all escaped by way of the Underground Railroad and have jobs in a tavern. Jemma's happiness is dampened only by the death of Sally Smith, the woman she considered her grandmother though they were not biologically related. As the novel comes to an end, Jemma reveals she has chosen the name Strong as her last name. Her young suitor, a former slave named Nathan, has chosen the surname Gardener. While Jemma says she needs time to get used to her own name, she feels that Jemma Strong Gardener has a nice ring to it.