The last summer before they go off to college, four girls renew their close friendship that centers on a pair of jeans they share to keep their friendship alive when they are not together. Girls in Pants is a story about growing up and maturing. It is a story of conquering fears that stand in the way of the next step to adulthood. It is the story of four girls who are very different but who share the need to identify significant truths about themselves and to move past these realizations and into the future.

The four girls, Tibby, Lena, Bee and Carmen, begin their summer by conducting a ceremony they have created which centers around a pair of jeans they pass around. There is a very strict set of rules that guides when they wear the pants, and they all imagine that magical things can happen to them when they have them on.

Lena is very conservative, and she begins the summer by going into a depression and isolating herself from those who love her most. Her strongest desire is to go to art school, and she takes a drawing course during the summer vacation. Through her drawings of her family, she begins to see what she never has seen before in each of them. By truly understanding her family, she begins to understand herself and begins her journey to freedom from her fear of failure.

Tibby does not think much of herself, and she thinks she is capable of almost nothing. A series of events forces her to rise above what she thinks she can accomplish, and through these accomplishments, she gains her own self-respect. When she does this, she can more clearly see the boy she has grown up with since childhood as someone she can love in a new and different way.

Carmen finds out that her mother is pregnant by her new husband. Carmen feels she will be left out of the family when the baby comes, especially when she goes away to school in the fall, so she decides to forego her dream of Williams College and go to a local school. When the baby finally comes, she realizes it will be an addition to their family and not a deterrent to her mother's love and attention. With this knowledge and security, she is able to love a boy she has recently met who seems perfect for her, and she allows herself to go away from home to Williams.

Bee met a boy two years before at soccer camp, and she has secretly loved him ever since then. When she finds she will be spending a lot of time with him during this last summer before college, she is scared that she will not be able to work with him and be his friend due to her feelings for him. Her fear has been to let herself admit to her feelings, and as a result, she cannot be the loving person she wants to be. When she learns to release the feeling she has tried to suppress, she becomes the person the boy she loves is looking for, and they are able to express their true feelings for each other.

At the end of the summer the girls get together and relate their experiences. They realize how many more people are in their intimate group. They vow to stay in touch forever, no matter what may happen to them.