Book three, The Promise, begins when Gracie and David take off for their honeymoon in her Uncle Rich’s RV. As they get to their first stop near St. Louis, Gracie gets a phone call from her cousin Angela. She says she has something for them—Great-great-grandma Mary's Wedding Ring quilt, made during WW1, as well as a Hope Chest with a false bottom. When she arrives, she and her husband Judd also bring along some great BBQ. Gracie and David investigate what happened during the first World War to a group of soldiers from Jubilee Junction and how the war affected those back home, including Grace’s great-great-grandmother Mary, the other narrator.

It's 1917. Mary Carlson is a senior in high school. She has her first romance with Charlie O'Connor who wants to marry her. However, with WWI raging in France, her whole town is concerned that many of the young men are about to be sent overseas. Her big brother and Charlie's big brother are both deployed with him, along with his best friend. So she comforts herself that they will look after each other.

Scenes from Book Three's setting during the 1917 entry into the Great War. Mary Carlson's family owns the town's General Store. She has relatives who live on the farm, as does Charlie O'Connor, her boyfriend. When America enters the war, Charlie and Mary get engaged. He prepares to leave for training, and so does his older brother Liam and her older brother Bruce. After Charlie leaves, Mary starts helping at the store. 

Mary spends an hour each day working on the linens for her hope chest, along with her younger sister Anna, her mother, and their grandmother Carlson. They also work on a double wedding ring quilt for her hope chest. 

Each week Mary goes to the Jubilee Public Library and meets her friend Ruby there. Ruby is Black and has educated Mary about the role of Black women in suffrage. She also has several cousins who are deployed with the 'Buffalo Soldiers," and shares their struggle for acceptance by some white soldiers and officers. 

Mary's Aunt Eva lives in Chicago and works as a nurse and is an avid suffragette (shown in hat, below). She invites Mary to come for a weekend, and Ruby comes along. They attend a meeting of the Alpha club and get to hear Ida B Wells speak.