The movie starts with Sardar Udham entering London in what is a closely plotted plan to take revenge for the Jallianwala Bagh massacre. However, the story often shifts focus from one timeline to the other. The latter was the Governor-General of Punjab in 1919. It was the inhumane Michael O’Dwyer who gave the deliberate orders to violently curb the peaceful gathering in Amritsar's Jallianwala Bagh.
However, everything gets personal when Udham Singh arrives at the Jallianwala Bagh hours after the massacre. The daunting look of the Bagh infuriates him with hundreds of dead lying in the blood pool. He also witnesses his love of life murdered there.
That is when he decides to join hands with Bhagat Singh and the Socialist Party and his aim shifts to revenge against the person responsible for it. Sardar Udham reaches London to assassinate him. There he gets help from various fighters from the Indian community. The Indian revolutionary fighter gets close to O’Dwyer after working for him. The whole story then revolves around the assassination and Udham's imminent arrest by the British Police and his persecution at the hands of British imperialist forces.