In a stunning milestone for justice in Central America, a Guatemalan court recently charged former dictator Efraín Rios Montt with genocide for his brutal war in the 1980s — and Pamela Yates’ 1983 documentary, When the Mountains Tremble, provided key evidence for bringing the indictment. Granito: How to Nail a Dictator tells the extraordinary story of how a film helped tip the scales of justice.