At Fort Concho, an army post in the American West, a supply wagon is robbed. Lt. Jim Ravencroft points to evidence that Shoshoni Indians are involved. The commander of the fort, Major Gaskill, orders Ravencroft to track down the stolen supplies; otherwise headquarters in Washington may dismiss him. Since most of the fort’s officers are engaged in the patrol, Private Jeff Reid is assigned to meet the stagecoach carrying Millie Gaskill, the Major’s daughter, in the town of Junction City and transport her to the fort for a party celebrating her engagement to Ravencroft. That same day Amos Tucker and Theodore Ogelvie, former bandits turned law-abiding citizens, ride into town on their donkey Clarise. After buying new suits and having their photograph taken, they decide to deposit all their money in the bank; however they are unaware that the man who greets them at the teller window, Wes Hardin, is in the middle of robbing the safe with his sidekick, Frank Starrett. Outside the bank, a nosy local, Tough Kate, spots the two robbers leaving the scene with bags of money strapped to Clarise, which they have also stolen, and screams for their arrest. While Starrett and Hardin gallop away, Woolly Bill Hitchcock, the town’s pompous marshal, enters the bank and mistakenly suspects Amos and Theodore as the culprits. After accidently wounding Hitchcock, the innocent twosome flees. Recalling that they described themselves as the Apple Dumpling Gang, the town photographer shows Hitchcock the picture he took of Amos, Theodore and their donkey, which Tough Kate identifies as the same animal she saw hauling bags of loot. While Theodore and Amos hide in a barn, Clarise comes in with the money still strapped to her saddle. In order to clear their names, Theodore devises a plan to abandon Clarise, since she was spotted assisting in the robbery, and to give back the money, but in the process of executing the plan, Hitchcock is injured again because of Theodore’s clumsy, yet well-meaning scheme. Although the stolen money is returned, Hitchcock vows to seek vengeance on the two Dumpling members. To track them down, he follows the trail of their loyal donkey Clarise. Avoiding detection, Amos and Theodore hide underneath the canvas of Jeff’s wagon next to cases of champagne. When Jeff and Millie reach Fort Concho, Ravencroft discovers Amos and Theodore drunk in the back, and Sgt. Slaughter begins the arduous process of recruiting them into the army. During the middle of the night, Jeff attempts to investigate evidence about the raids, but while sneaking away with an Indian arrow, he is caught and locked up in the fort’s jail by Ravencroft. At the engagement party, Amos and Theodore are carrying a punch bowl when Hitchcock unexpectedly arrives, accompanied by Clarise. In the resulting chaos, a lantern is knocked over, starting a fire. Inadvertently, Amos and Theodore cause the flame to spread throughout the fort, burning most of the buildings to the ground. In the aftermath, they are court-martialed and sentenced to thirty years of hard labor at a military prison. Because of the incident, Ravencroft will replace the Major as commander of Fort Concho. Meanwhile, Jeff escapes to a cabin in the mountains after being released from the fort’s brig during the fire. Using his real identity, Captain Phillips from U.S. Army Intelligence, Jeff meets with Sherick, a fellow undercover officer disguised as a trapper, and informs him that he still has no solid clues in the supply raid investigation. After Amos and Theodore are transferred to the military prison, they learn that the real boss of the place is Big Mac. Sometime later, they stumble upon Mac’s hideout underneath the prison and overhear a plan to rob a train carrying army payroll. Impressed by the duo’s unorthodox shooting skills, Mac recruits them for the upcoming heist, ordering them to meet at the Variety Saloon in Buffalo Springs by noon. Theodore and Amos pretend to cooperate; yet they have no interest in associating with the gang. Once in town, they seek protective custody from the local sheriff, but the only law-enforcement officer close at hand is Hitchcock. As the noon rendezvous nears, Amos and Theodore disguise themselves as dancehall girls to avoid Mac and his gang. During their act, Clarise the donkey comes into the saloon, and Amos and Theodore escape with her through the back door, derailing Hitchcock on the way. To evade Mac’s gang again, they trade Clarise for a pair of Indian blankets and camouflage themselves as squaws before boarding a train. They realize too late that they are on the train targeted by Mac. Meanwhile, knowing that the army payroll is on board, Jeff jumps on top of the moving train in the hope of catching the army supply thieves. Further along the route, Mac stands by to receive the loot, along with the secret informer from Fort Concho, Ravencroft, who has been profiting from the army raids by providing classified information on key shipments. On board the train, three of Mac’s men take control of the guarded compartment containing the army payroll. Suddenly, Indians ambush the train and bring it to a stop. Nearby, they also corner Mac and Ravencroft. With the train, passengers and gang surrounded, the Indian chief explains that he is not interested in the money onboard, only the squaw blankets worn by Amos and Theodore. Calling it a “dirty white man’s trick,” the Indian complains that the donkey they traded ran away. When Mac’s gang pulls off the blankets, everyone laughs at Amos and Theodore dressed as dancehall girls. Watching from the top of a train car, Jeff witnesses Ravencroft’s alliance with Mac and announces that he and his outlaw friends are under arrest. Before Mac’s gang is able to respond, Amos and Theodore manage to detain them at gunpoint. Later, after receiving an honorable discharge, Amos and Theodore ride home on Clarise while reading in the local gazette how the real bank robbers of the Junction City burglary were caught, thus clearing the name of the Apple Dumpling Gang.