In Fond-du-Lac, Saskatchewan, Canada, trappers, hunters and travellers gather at "Lady" Jane's hotel ("Vive la Canadienne"). Royal Canadian Mounted Police Sergeant Malone is flirting with Lady Jane, while wealthy city man Edward Hawley is watching a French Canadian girl, Rose-Marie La Flamme, even though she's miner Jim Kenyon's sweetheart. Rose-Marie's brother, Emile, is searching for her, fearing she is alone with Jim. Wanda, a half-blooded Indian, dances close to Hawley, enraging her Indian lover, Black Eagle. Lady Jane's man, the cowardly "Hard-Boiled Herman", arrives at the bar. Jim arrives to greet Rose-Marie enthusiastically and explains to Sergeant Malone that he has given up his former wild ways because of his love for "Rose-Marie". Black Eagle claims some land (and the gold on it) belonging to Jim and Herman. Herman thinks that shooting Black Eagle will solve everything, but Jim prefers to use legal means, declaring that he will visit Black Eagle and show him the boundary line the property map. Sergent Malone and "The Mounties" warn Herman that they will not hesitate to enforce the laws.
Emile is going to take Rose-Marie with him to the trapping grounds at Kootenay Pass. He dislikes Jim and wants her to marry Hawley for financial security. Rose-Marie doesn't want to go, insisting to her brother that she is in love with Jim ("Lak Jeem"). Hawley plans to accompany Emile, but first he has to end his affair with Wanda. He plans to visit her at Black Eagle's log cabin and bribe her to stay away from him. Jim tells Rose-Marie that he will follow her to Kootenay Pass, and they will meet in an old house he calls a castle near a valley with a beautiful echo. According to legend, Indians would call down into the valley to the girls they wished to marry ("Indian Love Call").
Hawley meets Wanda at her cabin and tries to pay her off, just as Jim arrives with a map to prove his claim. Wanda sends Jim away. Black Eagle returns home and catches Wanda and Hawley embracing. He attacks Hawley, and Wanda stabs Black Eagle to save Hawley. Jim and Herman, unaware of the murder, follow Emile, Hawley, and Rose-Marie to Kootenay Pass. Jim and Rose-Marie communicate through their "Indian Love Call" (reprise). Emile tells Rose-Marie that she should marry Hawley because he could buy her all the "Pretty Things" she wants. Wanda arrives at Kootenay Pass and tells everyone that Jim is wanted for the murder of Black Eagle; his map was discovered near Black Eagle's body.
Herman continues romancing Lady Jane ("Why Shouldn't We?"). Hawley proposes to Rose-Marie, but she refuses him. He and a city girl whom he has employed, Ethel Brander, try to impress Rose-Marie with the glamour of city life in Quebec. Wanda leads an Indian "Totem-Tom-Tom" dance. Jim has received an offer from the Brazilian government to lead a mining project there. He asks Rose-Marie to come with him, even though it would be safer for her to go to Quebec and wait for him there. If she decides to come, they will meet at the "castle" and go to the United States to be married. If she does not, she should sing the Indian Love Call up the valley to him. Rose-Marie insists she will go with him; he leaves immediately, and she plans to follow twenty minutes later to avoid attracting suspicion. Sergeant Malone arrives with a warrant to arrest Jim for murder. Emile knows that Jim is hiding in the "castle". He tells Rose-Marie that he will not reveal Jim's hiding place to the Mounties if she will go to Quebec and marry Hawley. Holding back tears, Rose-Marie tells Hawley that she must sing the "Indian Love Call" to him, but she is really singing to Jim, telling him that she will not go with him.
Many months have passed. Rose-Marie is about to marry Hawley in Quebec, believing that Jim was the killer. Ethel Brander has convinced her that Jim murdered Black Eagle because he loved Wanda. Herman and Lady Jane have married, and they have a shop in Quebec. He still flirts with other women, but he catches her giving Sergeant Malone "Only a Kiss". Jim returns with Wanda intending for her to clear his name. But, seeing Wanda, Rose-Marie jumps to conclusions about Jim and Wanda. Rose-Marie tells Jim that she loves Hawley ("I Love Him").
The wedding preparations commence ("The Minuet of the Minute"), and Wanda jealously threatens Hawley. Sergeant Malone prepares to arrest Jim, who is hiding in Kootenay Pass, even though Malone is troubled by the evidence. Herman suspects Wanda and gets her to confess by pretending that Hawley has accused her of the murder. Jane interrupts them and incorrectly assumes Herman is cheating on her ("One Man Woman"). The wedding begins ("Doorway of My Dreams"), but as Rose-Marie walks down the aisle, Wanda publicly confesses to the murder and declares her love for Hawley. Everyone rushes to Jim's lodgings, and Rose-Marie goes to the pass to return Jim's "Indian Love Call". The lovers are finally united.