Henry Dunant, a young business man from Geneva, wants to built a dam to help the Algerian people and therefore travels to France to talk to Napoleon III. directly. But the emperor is fighting the Austrians in Northern Italy and thus Dunant follows him. Near Solferino he gets into a battle and witnesses that the wounded soldiers of both sides are left behind on the battlefield. Together with Doctor Louis Appia, also from Geneva, he tries to bring as many wounded men as possible into churches and schools. With his slogan "We are all brothers" he wins the hearts of the population and they help him.
Dunant writes about his helplessness in a letter to the nurse Cécile Thuillier, who organises a troop of doctors and nurses. His friend Samuel Lowenthal publishes these letters. Nevertheless, the French officers force Dunant to leave the country. He now searches for a way to evacuate the Austrian soldiers. With blood he paints red crosses on white dressings and linen and leads the wounded Austrians and his helpers savely through a battlefield.
After this events he goes on realising his vision of a neutral aid organisation, trying to change the world.