The novel opens with Carmen Lowell narrating in first person. She describes her bond with her best friends, Bridget Vreeland, Lena Kaligaris, and Tabitha “Tibby” Rollins. The girls’ mothers met in a prenatal aerobics class at Gilda’s gym, and they’ve been inseparable since birth. Even after the bonds between their mothers dissolved, they remain close. Carmen says that each of her friends fits into an archetype: Bridget is athletic, Tibby rebellious, and Lena beautiful. She’s unsure where she herself fits.

Carmen introduces “the Traveling Pants” (11), a pair of blue jeans that she found in a thrift store that somehow fit each girl perfectly. All four girls share the pants, seeing them as a symbol of their commitment to remaining friends forever.

Carmen, Lena, Bridget, and Tibby gather in Carmen’s room to help her pack for her upcoming trip. It will be their first-ever summer apart: Carmen is headed to South Carolina to visit her father, Bridget to Baja California in Mexico for soccer camp, and Lena to Oia, Greece, to visit her grandparents along with her little sister Effie. Only Tibby is staying home in Bethesda, Maryland, to work at Wallman’s, a local drugstore.