Four teenage girls—Lena Kaligaris, Tabitha "Tibby" Tomko-Rollins, Bridget Vreeland, and Carmen Lowell—who are best friends and have been together all their lives in Bethesda, Maryland, but are about to separate for the summer. Lena is spending the summer in Greece with her grandparents; Tibby is staying at home; Bridget is going to soccer camp in Baja California; and Carmen is visiting her father in South Carolina. The girls go browsing at a local thrift store before they separate for the summer. They convince Tibby to try on a pair of jeans, which in turn Tibby makes Lena try them on, then Bridget, then Carmen; they find that the Pants magically fits all four of them perfectly, even though they have different measurements. The girls decide to share the Pants equally among them over the summer as a way of keeping together when they are apart. Lena, Tibby, Bridget, and Carmen part the next day, and the film focuses on each girls' journey separately.