In 1865, Aubrey Filmore works as a bell boy at the Palmer Hotel in St. Louis. Aubrey wants to work as a spy for the Union Government, and contacts Colonel Clifford M. Baker at the Union Secret Service, to ask if he can be of service in their elite spy unit. Aubrey has asked before, and the answer from Colonel Baker is still no. Posters are soon put up, warning the public of a particularly cunning spy named The Grey Spider. Aubrey sees the posters, and when Major Jack Drumman comes to stay at the hotel, Aubrey finds out that he is in fact The Grey Spider. Unfortunately Aubrey is discovered by the major, and tries to force him to wear Confederate clothes to look like The Grey Spider, in order to shoot him as a spy. Before the major's plan is realized, Aubrey accidentally knocks him unconscious. Major Drumman's dangerously alluring accomplice, Sallyann Weatharby, enters the room and Aubrey instantly falls in love with her. Since Drumman is knocked out, Aubrey agrees to join Sallyann, posing as the Major, to a meeting with other important Confederate spies. Before Aubrey leaves the hotel, he leaves a message for Baker, telling him of his plans. Aubrey is then involved in a complicated scheme to intercept the Union forces, and is given the important task of delivering the Union battle plans to the Confederate General Watkins. He is ordered to meet up with Sallyann at a hospital near the front, Morgan's Landing. Upon returning to Colonel Baker with the plans, Aubrey helps to make fake plans to replace the real ones with, and is ordered by the Colonel, who is very reluctant to involve Aubrey at all, to continue posing as Drumman and also deliver instructions to a Union spy. Aubrey mixes up the plans and the instructions, and manages to wear both Confederate and Union uniforms at the same time, resulting in that he is shot at by both armies and is knocked unconscious. He is carried to Morgan's landing, and Sallyann is there waiting for him as planned. With Sallyann is also her jealous fiancé Kurt Devlynn, who is also involved in the spy business. Since Sallyann has fallen in love with Aubrey, she tells Kurt she now loves Drumman. Aubrey then wakes up and manages to find the lost instructions to the Union spy and escapes the hospital. Kurt tells his men to dress in Union uniforms and intercept Aubrey/Drumman to steal the battle plans. Sheer dumb luck makes Aubrey escape from their clutches. When arriving to his destination at Sallyann's father's plantation, Aubrey by mistake delivers the wrong documents - the spy instructions instead of the plans - and mayhem ensues, where both Union spies and Confederate spies steal and retrieve the plans respectively. Ultimately General Watkins gets the plans and Aubrey's Union spy contact Captain Lorford gets the instructions. All is well. That night, Aubrey is busy courting Sallyann, when he is supposed to steal back the plans from the general. The Confederates realize there is a Union spy in the house and set a trap to catch him. But instead of catching Aubrey, they only manage to catch the real Grey Spider, Drumman, believing he is a Union spy. Since everyone thinks the Union spy is caught, Aubrey has no trouble getting the plans from General Watkins. But soon after, Drumman's father turns up and exposes Aubrey for what he is. When Aubrey is brought outside to be executed for treason, he is saved by Sallyann, and at that moment the war is declared over.
