At the end of the Civil War, in the New Mexico territory, cowboy Gil Kyle rides to Golden Trail, after being attacked by two men looking for Confederate sympathizers, or Copperheads. In the pro-Union saloon, politically neutral Gil attracts the attention of Candace Bronson, who flirts with him, then asks, "How many Mondays in a Thursday?" When Gil acts perplexed by the redhead's question, Candace excuses herself and goes to a back room, where she repeats the sentence to a waiting stranger. The stranger utters the words, "Broken sombrero, 13, 26," then falls dead from a knife wound. Having heard the fall, Gil enters, followed by the sheriff and a man named Dunn Jeffers. While the sheriff is interrogating Gil about the dead man, Candace sneaks off, leaving Gil without an alibi. Gil grabs Dunn's gun and flees on his horse, just behind Candace. On the trail, Gil intercepts Candace, who promises to clear him once she has reached her destination. Spotting the sheriff's posse approaching, Gil and Candace take off, riding all night until they come to a ranch house. Inside they find a dog lying on the dead body of rancher Carson. After Candace finds a note pinned to Carson, which reads, "Death to Copperheads," Gil surmises that she is a Confederate spy and kisses her. Just as Gil notices that the dog's collar has the Lazy Y brand on it, Dunn rides up, claiming he has come to buy Carson's cattle. While a suspicious Gil questions Dunn, Candace slips away. Dunn then claims that he, too, is a Copperhead spy and threatens to turn Gil over to the approaching posse unless he takes him to Candace. Gil and Dunn elude the posse and ride to the Lazy Y. There, they meet little Mary Barrett and her mother and father, who claim no knowledge of Candace. As Gil and Dunn are leaving, however, Mary gives them an Indian doll, noting that earlier she had given one to a "pretty lady." Gil and Dunn conclude that the doll is a Copperhead signal to go to a trading post near Ft. Jackson, and with the posse still pursuing them, head there. Farther up the trail, Candace, meanwhile, is forced to stop at a deserted cabin when her horse gets a rock stuck in its hoof. Two men, Brock and Perry, who have been following Candace, corner her in the cabin and, aware she is a spy, offer her a deal if she reveals where she is going. Before Candace can respond, Gil and Dunn show up and overwhelm Brock and Perry, whom Dunn identifies as mercenaries. After Dunn sends Gil and Candace outside, he tells Brock and Perry to follow him, then pretends to shoot them. Upon arriving at the trading post, Candace displays the Indian doll and says the code words. Candace, Gil and Dunn are taken to see Lamartine, who claims to be a Confederate colonel, and Candace finally delivers the "broken sombrero" message. Later, Lamartine reveals to the trio that the message has to do with a Union gold shipment, which he and his men plan to steal. Lamartine then exposes Dunn as a Union intelligence officer. In turn, Dunn calls Lamartine a renegade and accuses him of wanting the gold for himself, not the Confederacy. Lamartine dismisses Dunn's claim and orders Brock and Perry, who have been captured by his men, to be executed. After sending Candace off to his camp, Lamartine locks Gil and Dunn in a room and instructs his henchman, Munroe, to kill them once Lamartine has left the post. Gil and Dunn manage to escape the room but are immediately confronted by a gun-wielding Munroe. Having told Gil the gold shipment's route, Dunn instructs Gil to flee, then exchanges fatal gunfire with Munroe. Gil races to the Union camp and informs Capt. Andrews about Lamartine's plan. When Lamartine's soldiers, dressed in their Confederate uniforms, attack the Union wagon train the next day, they are met with equal force. During the bloody battle, Gil rushes off to find Candace, who is being held in Lamartine's wagon. As Candace and Lamartine fight for control of the racing wagon, Gil jumps on board and overpowers Lamartine. After the renegades are defeated, Andrews allows Candace to go, and she and Gil look forward to a happy future together.
