Benjamin Ferencz was 27 years old and had no trial experience when he became chief prosecutor at the Einsatzgruppen trial, one of the twelve subsequent Nuremberg proceedings, charging 22 SS commanders with the murder of over a million people. He had come to Germany as a US Army investigator right after the camps were liberated, gathering documents, and stumbled onto the death squads' own meticulous records of their killings. Director Ullabritt Horn follows Ferencz, then in his final years before his 2023 death at 103, to appearances in Washington, New York, Frankfurt, and Nuremberg, where he keeps making the case he first made in that courtroom: that law, not vengeance, has to answer atrocity. Interviews with colleagues and friends fill in the decades between Nuremberg and 2002, when his lifelong push for a permanent international court became the International Criminal Court in The Hague. The film moves between archival footage of the trial and present-day scenes of an old man still arguing the same point with undiminished energy.