The year is 1859. Italy's Second War of Independence has broken out as a result of Sardinia's desire to separate from Austria. Italy now has an overwhelmingly powerful position, as it receives the support of its ally, France. However, the Austrian Army continues to fight back, by such means as trying to restore itself in Solferino in the district of Lombardy. The conflict grows tense. As is the case in such a situation, the number of dead and wounded soldiers on both sides continues to mount. An overflow of the wounded from field hospitals are kept at a church.

Henri Dunant, a traveler who is on his way from Geneva, Switzerland, to Paris, happens to pass through this battlefield in Solferino. He is greatly shocked when setting his eyes on this graphic scene that tells the tragedy of war. As he stands watching dumbfounded, an injured Austrian soldier clings to his feet, begging for some water. Dunant has heard about a nearby church serving as an emergency field hospital. So he races there in a bid to save the life of the still-breathing solider.

On this day as well, injured soldiers are being carried into San Nicola church one after another. Not only doctors and nurses but nuns as well are rushing around to deal with the situation. Holding the injured soldier, Dunant runs inside. However, a nurse, Henriette, notices the soldier's Austrian uniform and immediately refuses to provide any treatment. She harbors hatred for every Austrian alive, as her parents had been murdered by Austrian soldiers right in front of her. She engages in an argument with Dunant, who insists that it doesn't matter whether a person is an enemy or an ally-that all lives are precious and should be saved. The Italian divisional commander, Manfredo Fanti, and the chief of staff of the Italian Army, Andrea Pollino, appear. They let Dunant know that out there on the battlefield-where winning and losing are a matter of life or death-he is being nothing but a bother with his views on justice.

Even so, an exasperated Dunant asks the doctor, Jean Hector, to let him help out in any way possible. Hector, as well as many of the other doctors and nurses, do have a heart, and they're carrying out treatment on wounded Austrians in a yard behind the church. But one day, Henriette and Pollino witness what's going on. Furthermore, they get wind of a wounded Austrian prisoner plotting to escape. An Austrian general, Leonid Benedeck, is shot and executed after taking full responsibility.

On another day, Henriette sets off with another nurse to the distant region of Mantova to get medicine and medical supplies. While cutting across a dangerous battleground, Henriette is shocked by what she sees, knowing full well the tragedy of war, even though her heart fails to open toward the Austrian soldiers. However, her heart gradually starts to become moved as she's exposed to the various beliefs held by the people around her-Dunant, Hector and Dr. Reniol Habermann.

Large numbers of the wounded are brought into San Nicola church every day. Its equipment and staff are now being stretched beyond their limits. The church has fallen into a situation whereby the wounded who should be given treatment and saved cannot help but become victims. Seeing this happen, Dunant has a plan that no one has ever thought of.