Fred P. Willis, a carnival barker, meets Jimmy Davis, an insecure accountant, just as the two enter the army at the beginning of World War I.  Jimmy has difficulty with army life, especially using a weapon.  He wants to desert so that he won't have to kill anyone, but Fred slugs him, then later convinces him to stay on.  Soon Jimmy becomes the best shot in his outfit and yearns for "moving targets."

When the unit goes to France, Jimmy becomes a hero when he is wounded after shooting several German soldiers, and no one knows that he shot one of them after the soldier raised his hands in surrender.  In the hospital, while recuperating from his wounds, Jimmy falls in love with nurse Rose Duffy, who is fond of him, but is really in love with Fred.  Fred returns her love, not realizing that Jimmy is completely dependent upon Rose.  When Fred is reported killed in action, Rose accepts Jimmy's proposal, not revealing that she loved Fred.  Fred soon returns, however, having only been missing in action, but when Jimmy says that he would die without Rose, Fred decides to give her up.  When Rose visits him, he pretends that he is already married and sends her away.

Some years later, Fred runs into Jimmy on a street in New York, just after a gang shooting has occurred.  Fred is suspicious that Jimmy is a hired killer when their old platoon leader, Sergeant Meadowlark, now a policeman, also runs into him and tells him that the killer was an excellent shot.  Fred goes to see Jimmy and Rose and realizes that their prosperity comes from murder.  He tries to convince Jimmy to stop, but Jimmy says he finds killing gangsters easy after the government ordered him to kill decent soldiers.

Rose goes to see Fred after learning that he was never married and Fred tells her that Jimmy is a hired killer.  Later, after overhearing him plan a job, Rose anonymously reports Jimmy to the police.  Although angry at first, Jimmy confesses to attempted murder in court, making Rose proud of him.  She says that she will wait for him and he goes to jail.  Fred and his friends at the carnival help Rose get away from Jimmy's gangster pals and she becomes one of the carnival workers.

While Jimmy is in prison, he becomes embittered after listening to a fellow inmate accuse Rose and Fred of infidelity and the two men escape.  He goes to the carnival and realizes that Rose has been faithful, but when he also realizes that they have secretly loved each other since France, he rushes towards the police who are trying to apprehend him and is killed when he fails to raise his hands in surrender.