On a warm evening in a Portuguese resort, a three-year-old girl vanished from her holiday apartment while her parents dined nearby. The disappearance of Madeleine McCann became the most famous missing person case of the 21st century. This episode dissects the anatomy of an international mystery, examining the catastrophic failures of the initial investigation, the blinding glare of media scrutiny, and the competing scientific theories that have left a family, and the world, searching for answers for nearly two decades.