The story opens with Caleb, a young boy, asking his sister, Anna, about their mother. Their mother had passed when Anna was young, and Caleb was just born. Caleb and Anna both miss their mother and wonder why their father, Jacob, doesn’t sing anymore. Jacob says he has forgotten the songs, but there may be a way for him to remember them. He tells the children he has put an ad in the newspaper for a wife, and Sarah Wheaton, from Maine, has responded. The children eagerly write letters to Sarah, and she responds to each separately.
Sarah agrees to come for a month, as a trial. On the day she arrives, Caleb and Anna are nervous and excited. They worry she will be lonely for her home. Sarah brings the children gifts from the sea, and her own collection of shells.
Winter turns to spring, and Sarah fits in perfectly. She picks flowers, makes meals for the family, cuts and grooms hair, and most importantly, she sings. Throughout, Sarah always talks about the sea. She sketches pictures of the ocean, but there is always one thing missing; the colors of the sea. Caleb and Anna feel that she is missing home and will leave them.
Matthew and Maggie, nearby neighbors, come to visit. Maggie and Sarah get along very well and find that they have many things in common. Maggie also moved to the prairie, to be Matthew’s wife. Maggie tells Sarah that she does miss her old life and the hills of Tennessee, but there will always be something to miss, no matter where you are.
The next morning, Sarah tells Jacob she wants to learn to do some of the things he does on the farm. She also tells him that she wants to learn how to drive the wagon, so she can go into town. This worries the children.
A storm comes and the family takes shelter in the barn. As the storm passes, Caleb points out that the sky looks like the colors of the ocean; the colors that are missing from Sarah’s sketch.
Jacob teaches Sarah to drive the wagon, and she takes it into town. Jacob works quietly for the day, while the children worry that Sarah will not return. They wait and fret until it is almost dark, when, finally, Sarah arrives back to the house. Sarah returns with special gifts, including pencils the color of the sea, so that she can finish her drawing. The children tell Sarah about their worries and she tells them that no matter how much she may miss Maine, if she were to leave, she would miss them more.