The movie is based on the young adult book, The Sisterhood of the Traveling Pants, by Anne Brashares. As four best friends spend their first summer apart from one another, they share a magical pair of jeans. Despite being of various shapes and sizes, each one of them fits perfectly into the pants. To keep in touch they pass these pants to each other as well as the adventures they are going through while apart.

A woman who has recently discovered that she is the daughter of Angelo, a major mafia boss, decides to wreak vengeance when he is killed by a hitman. She's aided by his faithful bodyguard, with whom she soon falls in love.

Two CIA agents, Tuck and Frank who are also best friends, have been benched because someone's after them. Tuck is divorced with a son whom he's not close to and Frank is a ladies man. Tuck decides to try and find someone so he places his profile on a dating website. Lauren, a woman also looking for a guy sees Tuck's profile and goes with him. She later bumps into Frank and he hits on her and she goes out with him. She's intrigued by both of them. When they learn that they're dating the same...