The book and the film tells the story of four inseparable friends who struggle with the realization that they won't be spending their summer breaks together. While shopping one day, they find a pair of jeans that magically fits each one of their body types, and they come up with the perfect plan to stay in touch: Each girl would wear the jeans and document her experiences in them before mailing them off to the next friend. It was kind of like sending a postcard, but instead of stashing the paper update in a drawer, you could pair it with a flirty summer top.