Two actresses serve the Union cause by spying in the South, but one falls in love with a Confederate officer in charge of spying.
After the Bull Run battles Gail Loveless (Marion Davies) sings at Ford's Theater and is recommended by Eleanor to Major Allen (Sidney Toler) as a spy. She becomes Operator 13 and disguises herself as a Negro maid doing laundry, talking with Confederate soldiers. Captain Jack Gailliard (Gary Cooper) spied in the north and is now in uniform as head of spying from Richmond. He meets Mrs. Vale, who is the actress Pauline Cushman (Katharine Alexander) spying for the north as Operator 27. Gail takes clothes to General Stuart and hears the plan, which she tells to Pauline after several songs by the Mills Brothers. Soldiers led by Captain Channing (Willard Robertson) find a federal pass in Mrs. Vale's house. Gail gives the information to traveling Dr. Hitchcock before she is taken as a witness in the spy trial. Gail says Pauline is a Yankee actress, which they already knew; but she helps her to escape. The Confederate attack is met by a cannon barrage as they try to cross the Potomac River. In Washington Pauline and Gail ask Major Allen for a bath.
Gail now blonde again is told of spies trying to organize a confederacy in the midwest, and they suspect Gailliard. Gail is deported south as the Confederate sympathizer Ann Claiborne. Gailliard is told to find out about her at the Shacklefords. There Gail learns of a battery placement at Drury Bluffs. Gailliard arrives and walks with Gail. On a swing she sings "Once In a Lifetime." She passes word of the battery. Gailliard dances with her at a wedding. Union cannon fires on the battery. The bride learns the bridegroom is not coming, because he was killed. Gail cries and tells Gailliard she hates war. They say they love each other. Captain Channing informs Gailliard that Ann Claiborne is in a northern prison. Gailliard looks for Gail, but she rides off in a Confederate uniform as he is wounded. He finds her in an empty house and wakes her up to arrest her, blaming her for being a woman spy. They watch Union troops execute Channing. Gailliard says Gail can call to them; but as fighting breaks out, they run off and break the handcuffs. Gail tells Gailliard to go, because she loves him.
After the war ends, Gailliard tells Gail that all must forget war, hatred, and division, and she says to remember loyalty and love.
Although Gail's initial disguise is absurd, this story does reflect actual incidents in the Civil War, and the romantic love makes the violence of war seem more absurd than anything else.