"Crash," a marshal working undercover, is arrested as a stagecoach robber and thrown in jail, but when his partner "Dusty" helps him escape, they allow Crash's cellmate, Red Langdon, to join them. Langdon takes them to Fugitive Valley, a hidden valley in which a gang of outlaws led by Gray has its headquarters. Crash, who is looking for a notorious outlaw known as "The Whip," immediately challenges Gray's authority, and when Gray beats him in a fistfight, he and Dusty are accepted into the gang. Crash and Dusty ask about The Whip, but are told by everyone that The Whip is no one man. To prove his mettle, Crash singlehandedly holds up a stagecoach which is carrying his other partner "Alibi," who is posing as a magician. Gray kidnaps Alibi to entertain his men, and Alibi uses his pigeons to send messages to a nearby marshal and inform him that they are now working undercover in Fugitive Valley. Dusty and Crash soon compete for the attention of Ann, the resident doctor's assistant, but she is suspicious of their questions about The Whip. When Ann slips out of Fugitive Valley, Alibi follows her to a secret cave, but cannot find the entrance. Inside, Ann meets with local ranchers, all of whom have lost their ranches because of Gray's raids, which have been masterminded by civic leader Brandon. Ann, who is really The Whip, a vigilante trying to avenge the death of her rancher father, has been using her position as the outlaws' nurse to gain information. She now knows that Brandon will be traveling to the bank with loot from Gray's most recent robberies, and plans to steal it back and distribute it among the ranchers. To this end, she hides behind a rock and uses her whip to disarm Brandon as he is riding by, and he is then robbed by Ann's masked gang. Brandon later visits the sheriff, who promises to eradicate The Whip, and becomes suspicious when a pigeon flies in the jail. After Brandon alerts Gray about his suspicions, Gray plans to entrap the infiltrators by falsely announcing a raid and waiting to see who will warn the sheriff. Ann learns about the raid and arranges for her posse to take over the outlaw's headquarters while the gang is out. Alibi warns the sheriff about the raid, and the next day while performing magic tricks, he, Crash and Dusty try to take the gang hostage. Crash and Dusty escape, but Alibi is knocked unconscious, and the gang rushes out to chase the marshals. After they leave, Ann brings her men in and finds money in Gray's safe which matches the bills stolen from her father before he was murdered. The sheriff's posse chases the outlaws back to the hideout, but they are locked out by Ann and arrested, and the sheriff returns to town to arrest Brandon. Later, Crash, Dusty and Alibi learn that Ann is The Whip and is working on the side of the law, and she learns that they are marshals known as The Range Busters. Although Crash and Dusty want to remain in Fugitive Valley, Alibi senses woman trouble, and forges a message from a friend requesting their help in order to draw them away.