The day after Anna's brother, Caleb, was born, their mother died. Anna and her father, Jacob, miss her terribly, and young Caleb has never known what it is like to have a mother. So Jacob decides to advertise for a wife and mother, someone to bring song and laughter back into their prairie home.

Sarah Elisabeth Wheaton from Maine answers his ad. After exchanging a few letters with the family, Sarah decides to travel west to spend one month with them. When the month ends she will decide either to stay and marry Jacob or to return to Maine.

Sarah arrives and both Caleb and Anna grow to like her; but the children worry that their home will not be "good enough" for Sarah. They can tell that Sarah is lonely and misses her home in Maine and the sea, and they are afraid she will not stay because of the things she would miss. As they get to know and care for each other, they find that they all must make adjustments to create a new family. Sarah also comes to realize that although she will always miss the sea, she would miss Caleb, Anna, and Jacob even more.