Calamity Jane (Jane Russell) is coerced by federal agents to go west and find out who is supplying guns and powder to hostile Indians. She is supposed to meet another agent, and join a wagon train pretending to be man and wife. When she gets there, she finds the other agent murdered. Three outlaws are after her to kill her. She ducks into a dental office run by "Painless" Peter Potter (Bob Hope) to hide. Painless gets knocked out, and she surprises the bad guys, killing all three. Potter gets the credit, and begins to get a reputation as a dangerous gunfighter.
Jane can not go west alone, so she tricks/ forces Painless to go with her in his wagon as man and wife. Along the way, they are attacked by hostile Indians. Potter is trapped outside, and begins shooting at the Indians. Jane is shooting from a hiding place and kills 10 Indians. The rest of the Indians flee. Again, Potter gets the credit.
When they arrive at the town, the gun smugglers know that a federal agent was supposed to be on the wagon train. They assume it is this "dangerous" gunfighter Painless Potter. They try to get a local tough guy to kill him in a duel. Again, Jane shooting from a window kills the guy, making it look like Painless won the duel. The bad guys decide to get out of town quickly with the guns and powder. Jane tricks Painless into going to stop them. They take him and Jane prisoner and take them along to the meeting to deliver the guns and powder. The Indians want to torture and kill Painless in retaliation for the 10 Indians killed earlier. Due to a mistake by the medicine man, Painless escapes. Before his escape, Jane confesses everything to him, apologizes for getting him into this, and proclaims she loves him. After his escape, he realizes he loves her too, and returns to rescue her.
The Indians are going to burn Jane at the stake. Painless dresses like an Indian and joins their ceremonial dance. Instead of a drum, Painless grabs a barrel of gunpowder. As he dances around, he trails gunpowder everywhere. He pretends to threaten Jane with a knife, but really cuts the ropes holding her. Potter is finally recognized, and they tie him up to be burned at the stake also. When they go to light the fire, the gunpowder ignites. As the flame follows Painless's gunpowder trail, the entire Indian village goes up in flames. The guns and powder are all destroyed. Jane and Painless escape in the commotion.
At the end, Painless and Jane are married. (All through the movie, Painless keeps unhitching the horses, and forgetting that he did so. When he tries to start moving, the unhitched horses pull away from the wagon dragging him behind them. As Painless and Jane leave on their honeymoon, she tells him to let her drive this time. The unhitched horses take off, dragging her down the street behind them.)
Thanks Joseph C!