A regiment of the Union army rests through a cold spring, trading rumors about whether it will finally move. Among the men is a youthful private, Henry Fleming, who had enlisted against his mother's quiet wishes, full of dreams of Greeklike struggles and his own eagle-eyed prowess. Now, facing a real battle, he is gripped by a question he cannot answer: when the moment comes, will he run?
The regiment is thrown into combat. In the first assault Henry holds his place and even feels the fierce, animal solidarity of men fighting together. But when the enemy comes a second time, panic spreads, and he throws down nothing of his resolve and simply bolts, running like a rabbit toward the rear while convincing himself it was the act of a superior mind reading the field correctly.
Wandering behind the lines, he joins a grim procession of the wounded and meets a tattered soldier who keeps asking, gently, where Henry himself is hurt. He watches his friend Jim Conklin, the tall soldier, stagger off to die in a field, and he abandons the failing tattered man rather than face that question. He begins to envy the injured and to wish for a wound of his own, a red badge of courage to prove he belonged in the fight.
His wound, when it comes, is delivered by accident: a terrified Union soldier in a rout swings a rifle and cracks it against Henry's head. A cheery stranger guides him back to his regiment in the dark, where his comrades assume his bloody scalp is an honorable battle injury. Sheltered by that misunderstanding, and stung by the memory of the men he failed, Henry returns to the ranks changed.
In the next day's fighting he turns reckless, seizes the regimental colors, and leads a charge with a fury that wins praise from the officers who had scorned the regiment. At the close he looks back on both his cowardice and his courage and quietly puts the brass and bombast of his old dreams aside. He has touched what he feared and found it was only death, and he walks on feeling, without much fanfare, that he is at last a man.