"Captain Miller" follows the story of a man who turns against the British-led Indian military after witnessing atrocities. The protagonist, Analeesan 'Easa' (played by Dhanush), takes a stand against the injustices perpetrated by the colonial forces. As he rebels against the oppressors, Easa becomes known as Captain Miller, leading a courageous fight for justice and freedom. The film explores themes of bravery, sacrifice, and the quest for liberation in the face of tyranny.