In 1917, at Camp Mills, New York, Major "Wild Bill" Donovan swears in the new recruits of the fighting 69th New York regiment, among whom is Jerry Plunkett, an arrogant braggart who refuses to follow orders. Once sent overseas, Plunkett becomes even more belligerent, and not even the unit's beloved Chaplain, Father Francis Duffy, can bring him back into the fold. Despised by the other men, Plunkett causes a massacre at Rouge Boquet when he disobeys orders and inadvertently incites the Germans to attack. Disgusted by Plunkett's behaviour, Donovan wants to transfer him out of the company, but Duffy convinces the Major to give him another chance. Although a bully in camp who brags about coming home "dripping with medals," Plunkett is a coward in battle, and after he becomes hysterical and alerts the Germans to the company's location, thus causing more deaths, he is court-martialed and sentenced to be shot. Meanwhile, the rest of the regiment is ordered on a suicide mission to take the sector at the Argonne without military support. As the regiment is beseiged by shells, the jail in which Plunkett is imprisoned is bombed and he escapes. Dashing to the hospital, Plunkett witnesses Father Duffy leading the wounded in a recitation of the Lord's prayer, and discovers in himself the faith that the father had preached. Speeding to the front, Plunkett launches a daring attack with a trench mortar, blasting a hole through the barbed wire and thus allowing the regiment to capture their objective. In the attack, Plunkett is fatally wounded, but before he dies he is given the last rites and hailed as a hero.