In November 1864, during the final weeks of the American Civil War, a Union train pulls into Greensburg, Ohio. Beside passengers, troops and mail the train also carries the latest military invention of Dr. Gatling, the Gatling Gun. Only four such weapons have been assembled and one of them is being sent out West to be tested by Union troops. However, Confederate spies, led by Captain James S. Simmons, of the Georgia volunteers, are well informed regarding the presence of the Gatling Gun on the train. The Confederates, masquerading as Yankees, have set-up an ambush at Greensburg's railway station. When the train stops at Greensburg, the Confederate spies manage to attack and capture the crates containing the disassembled Gatling Gun. After leaving the scene, the Confederate team disperses and only Captain Simmons and Sergeant Guderman carry the Gatling hidden in an elixir salesman's wagon. The two Confederates must cross all Union states undetected and reach Confederate lines with the Gatling Gun. At a river crossing they meet a female doctor in an ambulance wagon that has broken down. The Confederate spies hesitate about helping the Yankee woman for fear of blowing their cover. But the Southern manners win and they decide to help her. They also hide the crates containing the Gatling Gun in her ambulance. In the Yankee town of Baxter Springs they take the doctor and her patient to her home-clinic where they hide the Gatling Gun in a chest in the dinning room. This way they can roam the town without being caught with the Yankee weapon in their possession. They also must find a Confederate sympathizer in town in order to be guided through enemy territory to the Confederate lines. Pretending to be elixir salesmen they sell bottles of muscle-building elixir in town. Arriving in town in a hurry, Union soldiers led by Lt. Braden and assisted by hired Pinkerton's detective Frank Kelso search the region to retrieve the gun. The task of the two Confederate spies has become more difficult, unless they find a contact man who can provide them with information and a guide to take them through Union lines and Indian territory to the nearest Confederate lines.