Through New Zealander Rob Hamill’s story of his brother’s death at the hands of the Khmer Rouge, Brother Number One explores how the regime and its followers killed nearly 2 million Cambodians between 1975 and 1979. In 1978, Kerry Hamill and two friends disappeared without a trace while sailing from Australia to Southeast Asia. Rob discovers that a Khmer Rouge cell attacked the boat. One sailor, Canadian Stuart Glass, was shot immediately, but Kerry and Englishman John Dewhirst were taken to the notorious S-21 Prison in Phnom Penh, held for several months, tortured, and killed. Thirty years later, Kerry’s youngest brother Rob has a rare chance to take the stand as a witness at the Cambodia War Crimes Tribunal and face Comrade Duch, the man who gave the final orders for Kerry and thousands of others to be tortured and killed. As Rob retraces his brother’s final days, he meets survivors who tell the story of the S-21 prison and of what countless families across Cambodia experienced at the hands of the Khmer Rouge. In this spirit, Brother Number One grapples with the trauma that grips all Cambodia: the struggle to forgive in the face of immeasurable anger.