A Summer to Die by Lois Lowry tells the story of thirteen-year-old Meg Chalmers whose whole life is turned upside down when her parents, Charles and Lydia Chalmers, tell her and her fifteen-year-old sister, Molly, that they will be closing up their family home in the small New England town where they live and moving to a country farmhouse. The girls are shocked, especially Meg who is shyer and more reserved than her popular and beautiful older sister. Meg has lived in their house her entire life. The girls are not happy that they will be leaving behind their school and their friends. But there is a silver lining, they will only have to live on the farm for a year while Charles finishes the book he is writing. He is a university professor and the school is giving him the year off to complete the important work.

One of the biggest disappointments in the new house is that Meg and Molly will have to share a bedroom. The situation causes some conflicts immediately because Molly is always as neat as a pin and Meg is on the messy side. There are other differences between the girls. Molly is beautiful and popular and no one can remember when she didn't have a boyfriend. Meg is shy and studious and does well at school scholastically but not socially. She envies her beautiful sister although she does like being smart and different. Molly wants to get married young and have six children. Meg has never even thought of marriage. She wants to be a writer or an artist or a photographer. Molly gets so upset with Meg's bad housekeeping that she draws a chalk line down the center of the room and dares Meg to cross over to her side.

Despite their differences, the girls do love and care for each other. Molly encourages Meg in her pursuits. She thinks Meg is especially talented in photography. Molly adjusts to the new school and within a month she's a cheerleader, has made a lot of new friends and has a cute boyfriend. The only notable thing that happens to Meg is that a boy in her class starts calling her Nutmeg and it sticks. Meg ventures out in the field one day and comes across an old man working on his truck in front of a small house. As it turns out it is Will Banks, the kind and gentle 70-year-old widower who owns the land and the houses on it. Meg and Will hit it off and become friends. In fact, she gets him interested in photography.

A young couple, Ben and Maria, rent one of the other houses on the land. They become good friends with Meg and Molly. Maria is expecting their first child and Molly is thrilled at the prospect. Molly falls ill with the flu in the middle of winter and experiences quite a few nosebleeds. But the nosebleeds don't stop and Molly has to be taken to the hospital. Molly stays in the hospital for an extended period while she undergoes a battery of tests. When she returns home, she is pale and thinner and her beautiful blond hair is falling out.

Charles and Lydia don't tell Meg just how bad Molly's condition really is. She continues to deteriorate and even though there are many signs that Molly is fading, Meg assumes she'll be fine and recover. Molly does not respond to the medications she is given and must be rushed to the hospital again one day. She never returns. Although Meg misses her sister and her life will never be the same, there is new life in the neighborhood. Maria has a baby boy and Meg is allowed to photograph it while it is being born. And she is also the first to hold it. There is new life in Will, too. He becomes so skilled at photography that his photos are featured in an exhibit in the university museum.

When Meg walks through the forest with Will to see a flower that is the last to bloom in the season, she pictures her beautiful sister in the tall grass, gathering wild flowers. Will wanted to show Meg that special flower because like she, it was a late bloomer.