Based upon the 1996 novel, Valentine: A Novel by Tom Savage, Valentine revolves around a group of best friends Kate (Shelton), Paige (Richards), Dorothy (Capshaw), Lily (Cauffiel) and Shelly (Heigl), who grew up together and scorned nerds while in high school and on the college campus.
Ten years later, the friends are still single but have careers and continue to seek out the perfect man. Kate is having an on-again/off-again relationship with Adam (Boreanaz), a sports writer. The others have similar relationships with other men.
After the women meet at a friend's funeral, they all start receiving strange, menacing Valentine messages. A detective investigating the death of their friend believes the letters are linked to someone they all knew and tormented back in junior high. As threats intensify, each must deal with the fact that any man she knows or knew may be a vicious killer.