Carmen, Tibby, Lena, and Bridget have been best friends all their lives. They live in the same small American town and usually spend every moment of their long summer holiday together. The year they turn 16 is the first time they have separate plans for the summer, but the girls are determined to keep in touch.

Carmen buys a pair of jeans in a second-hand shop, and the girls discover that the trousers magically fit each of them perfectly, despite their different figures and heights. They hit upon a wonderful plan of sharing the jeans throughout the vacation, sending them on to the next friend when they feel the time is right. From Baja, California, to Greece, from film-making to football, the girls and the travelling pants encounter first love, family upset, and fatal illness. Secure in the knowledge that their friendship is constant, and the symbol of it need never be more than a parcel-delivery away, the girls survive their summer and return home with a wealth of new experiences to share.