When 16-year-old Mark, a handsome and popular boy, meets local girl Rachel on the Internet, he quickly finds himself in an intense online relationship. Besotted, he will do anything for her - even befriend and defend her bullied, loner brother, John. When Rachel, who is trapped in an abusive relationship, is murdered, Mark and John are determined to avenge her death. Their actions draw the attention of a female MI5 agent as they unwittingly stumble into an ongoing operation. Soon, Mark is recruited to commit a devastating crime, one that made British legal history.