When a college student in Milwaukee vanishes after a first date, investigators race to retrace her final movements. Using data from an app on her phone, law enforcement begins to piece together where she went – and whom she was with. As the investigation focuses on a man named Maxwell Anderson, chilling security camera footage and evidence discovered on a secluded beach raise urgent questions about what happened to Sade Robinson. 48 HOURS correspondent Anne-Marie Green reports in "Sade Robinson and the Secret Beach."