When fourteen-year-old Ellie Parry is found murdered in a house on the Sofrydd Estate near Crumlin, Detective Inspector Marc Fagan is thrust into a complex investigation that quickly spirals into a deeper nightmare. Determined to bring the killer to justice, Fagan finds no shortage of suspects in Ellie's troubled family and social circle. But as the investigation unfolds, shocking truths about Ellie's life emerge, painting a far more sinister picture. Ellie's murder unravels a complex web of secrets and lies within her troubled family background. At the centre of the mystery lies a popular social media platform, Cymru-Teen-Chat, created by Welsh entrepreneur Russell Connor. As Fagan delves into the app's connection to Ellie's murder, he uncovers an alarming truth - the platform has been linked to the suicides of multiple young girls over recent years. As Fagan pieces together the tragic deaths, he stumbles upon a horrifying revelation: Ellie's murder is the work of a serial killer stalking the South Wales Valleys, preying on vulnerable teens.