In the 1870s, fugitive outlaw Johnny Drum is confronted by Sheriff Sam Borden inside a general store. Drum shoots the sheriff in front of customers Lin Conner and Julie Ann McCabe. The two women are saloon dancers and Julie happens to be the girlfriend of another wanted outlaw, Whit Lacey. He's wanted for raiding Eben Martin's mining operations. After escaping the town, Drum takes to the trail where he's followed by the sheriff deputies and their posse. He manages to elude them but he's attacked by a band of Sioux. Fortunately, Drum is aided in the ensuing firefight by bandit Whit Lacey who happened by. The two outlaws become friends and partners. They plan various robbery schemes. Lacey needs the money to move to California with his sweetheart, Julie Ann McCabe. Unknown to Lacey, Drum actually is an undercover army officer who only pretended to kill the town sheriff in order to create a cover story in his quest to find and apprehend Lacey. Eventually, Lacey finds out the truth about Drum but allows him to leave their hideout unharmed. Later, Drum and the town's deputies capture Lacey and take him to the nearest army fort. They want Lacey tried but some angry citizens at the fort want to lynch him, despite Drum's fierce opposition. The lynching is interrupted by a major Sioux attack on the fort. Now, they all have to forget their differences and defend the fort until reinforcements arrive. Drum and Lacey find themselves fighting, once more, side by side.