In the present, many Sikh volunteers under Khalsa Aid come to the Syria-Iraq border to help refugees. An elderly Sikh volunteer tells his volunteers (especially a curious girl) about Sajjan Singh Rangroot, Diljit Dosanjh, a soldier who fought in World War I.
In the early 20th century, Sajjan is a young Sikh man who dislikes the British. His father works for the British, and wants his son to work for them as well. As World War I unfolds, Sajjan hopes to serve in the British Indian Army, believing that a British victory could clear the path to India’s independence. His mother supports the dream, while his father remains wary. He joins the Lahore Regiment, and forges bonds with peers Dheera, Teja, Lachhman Das, and Mela Singh. The Subedar, Zorawar Singh, is a battle-hardened leader who pushes the unit through arduous training as they prepare for deployment to Britain.
When the regiment reaches Britain, British soldiers mock the Sikhs, but the men train on, keeping their pride intact. At a tea shop, Sajjan clashes with a British soldier; Becky, the shop's owner, intervenes to keep the peace and protect her business. Becky forms a soft spot for Sajjan, though he is already betrothed to Jeeti. The story follows their camaraderie as the unit encounters the brutal realities of trench warfare.
The trench action arrives: the Sikhs and their British comrades fight to reach a key trench as German forces press their advantage. They manage to secure it and even overtake the main German trench line, forcing a retreat. In the harrowing moments, Dheera is killed, and Sajjan carries the weight of the trauma. Subedar Zorawar Singh rallies Sajjan, urging him to press on.
A German letter arrives, tempting the Sikhs with better equipment, food, and pay in exchange for defecting. Sajjan refuses, preserving the bond with his comrades and the honor of his people.
As the attack resumes, Mela Singh signals that Baisakhi is near, but the mood is somber. Sajjan tries to lift spirits by singing a hopeful tune, only for Teja to fall in battle as the conflict rages on. He gathers his resolve and, crossing the battlefield alone, bombs the German trench. The mission succeeds, but Sajjan loses his life in the act.
Back home in India, both British and locals pay their respects to Sajjan Singh Rangroot for his sacrifice. In the present day, the elderly volunteer reveals a photograph of Zorawar, who turns out to be the grandfather of the storyteller, linking the wartime hero to the next generation. The Sikh volunteers leave with renewed resolve, inspired by Sajjan Singh Rangroot to serve others with courage and faith.
