Intended as a low-budget ‘bottle show’ to save money before the season finale, ‘Duet’ devotes most of its runtime to two characters steeped in conversation with each other. But this dense story and its tug-of-war between justice and vengeance have come to be regarded as one of the finest hours of Star Trek. The episode’s writers drew inspiration from the play ‘The Man in the Glass Booth,’ which in turn was inspired by the kidnapping and trial of Nazi war criminal Adolf Eichmann by the Israeli...