Jonathan Miller opens his three-part account of atheism by asking where disbelief actually comes from, and the answer he pursues runs from Ground Zero to Ancient Greece. He stands at the site of the fallen Twin Towers to weigh what the September 11 attacks did to religious certainty, then talks with playwright Arthur Miller and philosopher Colin McGinn about doubt as a personal and intellectual position rather than a slogan. The film goes back to classical Greece looking for the first recorded skeptics, the people who questioned the gods before atheism had a name, and sets their arguments against modern theories of why belief in myth and magic took hold so widely in the first place. Miller narrates in his own voice throughout, tracing the idea rather than staging debates, and treats disbelief as a history with real people and texts behind it instead of a modern controversy. This opening episode is titled Shadows of Doubt and lays the groundwork for the two installments that follow.