When 16-year-old Mark, a handsome boy, popular with girls, 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 awkward, loner brother, John, the perpetual target of school bullies. When Rachel, who is trapped in the grips of 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 on-going operation. Soon, Mark is recruited to commit a devastating crime, one that made British legal history.