A Southern Yankee

In 1865, Aubrey Filmore works as a bellboy at the Palmer Hotel in St. Louis and dreams of serving as a spy for the federal government. He reaches out to Colonel Clifford M. Baker of the Secret Service to offer his help. Baker refuses, telling him there is no place for amateurs in their elite unit.

Posters warn the public about the cunning spy called the Grey Spider. When Major Jack Drumman arrives to stay at the hotel, Aubrey realizes he is the Grey Spider, but the major traps Aubrey and tries to force him to wear Confederate clothes to resemble the Spider and shoot him as a spy. Before the ploy can be carried out, Aubrey accidentally knocks Drumman unconscious.

Sallyann Weatharby enters the scene and Aubrey quickly falls in love with her. He agrees to join Sallyann, posing as Drumman, to attend a meeting with important Confederate spies. The arrangement ties him to a risky gambit behind enemy lines.

Before Aubrey leaves the hotel, he leaves a message for Baker telling him of his plans. He becomes involved in a plan to intercept Union forces and is assigned the key task of delivering Union battle plans to Confederate General Watkins. He is ordered to meet Sallyann at Morgan's Landing, a hospital near the battlefront.

Upon returning to Colonel Baker with the plans, Aubrey helps craft fake documents to replace the real ones and is reluctantly ordered to continue posing as Drumman and to deliver instructions to a Union spy. He then accidentally mixes up the plans and instructions while wearing Confederate and Union uniforms, and both armies open fire on him before he is knocked unconscious. He is carried to Morgan's Landing, where Sallyann awaits as planned.

Sallyann's fiancé Kurt Devlynn, who is also a spy, is present. As Sallyann has fallen in love with Aubrey, she tells Kurt that she now loves Drumman, creating a tense triangle of loyalty and deception.

Aubrey wakes up, finds the lost instructions, and makes an escape from the hospital. The escape sets the stage for the next phase of the plan and its misdirections.

Kurt orders his men to dress in Union uniforms and intercept Aubrey, whom they believe to be Drumman, in order to steal the battle plans. The pursuit follows through the Confederate lines and into the plantation domain.

Arriving at Sallyann's father's plantation, Aubrey mistakenly delivers the spy instructions instead of the battle plans. Union spies seize the plans and Confederate spies retrieve them, while General Watkins and Captain Lorford react to the scrambled data.

That night, while Aubrey courts Sallyann, Confederates set a trap to catch a spy, but they end up catching the real Grey Spider, Major Drumman, who is mistaken for a Union agent. The dramatic capture adds to the confusion of loyalties.

As everyone assumes the Union spy has been caught, Aubrey manages to obtain the battle plans from General Watkins for the Union contact Captain Lorford. The plan reversal helps keep Aubrey's cover intact for the moment.

Drumman's father appears and exposes Aubrey as a spy pretending to be his son. Aubrey is brought outside to be executed for treason, but Sallyann saves him, and the war ends shortly thereafter.