As lone rider, Sandy Saunders travels through the Western desert, singing and playing his guitar, he sees an old man in the distance stumble. Finding that the man, Sheriff Bill Baxter, has been shot in the back, Saunders takes him to the nearby town of Starbuck. Later, from a height, Saunders sees a road agent hold up a stage. When one of the drivers shoots the robber's horse, Saunders rides down and finds the agent to be a woman, Fay Denton. He gives her his horse to escape and, impersonating the robber, eludes the bumbling stagecoach drivers. Fay returns to her home and gives her father, Dad Denton, the money from the stage, which actually belongs to them. Meanwhile, Saunders hides in the stage as the drivers ride to town and witnesses an attempted robbery, which fails because Fay already got the money, by men in cahoots with the drivers. At the Denton ranch, Dad explains that he and Fay own half interest in a mine at Yucca. The letters from their partner at the mine have been opened, and their shipments subsequently have been stolen from the stage. In addition, James Kincaid, whose men have been robbing the stage, owns the water rights to Lost Creek and thus controls all the ranchers except the Dentons, who have the only well in the area. Kincaid has threatened to cut off the ranchers' water supply when the present contract ends in three days unless they either sell their land to him at an outrageously low price or pay four times the previous price for water. Because of this, the ranchers have written to Washington for help. Saunders accepts Dad's invitation to stay with them, and after capturing two of Kincaid's men who try to ambush him, Saunders sings and plays guitar for Dad and Fay, who is growing fond of him. When the ranchers disregard Kincaid's threat, he orders his men to cut off the water supply from his dam. After the driver of a wagon filled with water from Dad's well for the other ranchers is shot by Kincaid's men, Saunders chases them away, stops the madly running horses and drives the wagon to town. Kincaid orders Saunders out of town and backs up his threat with his hired gunman Slip Morgan, but Saunders, in a showdown, shoots Morgan in the wrists so that he can never use a gun again. Word soon spreads that Saunders is really "Singin' Sandy," the most notorious gunman since Billy the Kid. After Fay hears this, she follows Saunders to Kincaid's office and overhears Saunders accept Kincaid's offer to become his gunman and Saunder's suggestion that they dynamite the Denton well. Saunders then meets with the ranchers and convinces them to accept Kincaid's contract on the condition that he includes a clause stating that if he fails at any time to provide water, his water rights and land will become community property. Kincaid agrees and new contracts are signed. Meanwhile, Fay tells her father what she overheard, and when they find Bill Baxter's badge among Saunder's belongings, they think that he killed Baxter. After Kincaid's men dynamite the Denton's well, water flows throughout the valley. Saunders reveals to Fay and Dad that he was sent from Washington and that he discovered that the well was the headwaters of Lost Creek. Baxter, who is due to arrive soon, made Saunders his deputy when Saunders came upon him in the desert. The ranchers frolic in the newly-formed lakes and streams. Kincaid shoots Morgan for not killing Baxter, and after a chase, Kincaid is shot by Saunders. He then falls over a cliff into his dam, where he drowns. Upset that she suspected Saunders and fearing he will leave, Fay is cheered when he kisses her and says he'll be back for supper if she'll be bake him a hundred of her biscuits.
