After suffering a great personal loss, 25-year-old Theodore Roosevelt abandons New York politics for the lawless Dakota Badlands, where he plans to become a cattle rancher at the height of the Beef Bonanza. The former politician must now navigate a dangerous path through the Badlands, where his youth and physical frailty make him an easy target. Upon arriving in the frontier town of Medora, he immediately squares off with a gunslinging bully. Time and again, Roosevelt must prove his strength on the forty-mile journey to secure the property for his cattle ranch. Along the way, he is haunted by memories of loss, and he survives a first encounter with a powerful and deadly landowner, the Marquis de Morés. With the help of his lumberjack mentor, Bill Sewall, and his cowboy partner, William Merrifield, Roosevelt establishes the sprawling Elkhorn Ranch. The adventures and hardships of building Elkhorn will transform the young Roosevelt into a true cowboy and set him on a path to greatness.

Theodore Roosevelt must fend off a powerful neighbor, the Marquis de Morés, who is intent on seizing Roosevelt’s newly built Elkhorn Ranch in an underhanded land grab. To save his ranch, Roosevelt travels to the home of the Marquis and his beguiling wife, Medora, who is just as cunning as her husband. Back at Elkhorn, Roosevelt’s new ranch hands, former lumberjacks Bill Sewall and Wilmot Dow, are attempting to master the saddle when their bronc-busting lessons are suddenly cut short by the arrival of the Marquis’ henchmen. For one long night, Elkhorn’s very survival hangs precariously in the balance.

Roosevelt’s efforts to prove himself a capable cowboy are off to a shaky start when he’s mocked by a loudmouthed ranch hand. On the spot, Roosevelt challenges the new hire to put up his fists or shut up. After Roosevelt proves his mettle, the two become fast friends. But soon, Roosevelt’s reputation takes another hit when a neighboring rancher accuses his men of rustling cattle. To save Elkhorn’s good name, Roosevelt and his men must capture the real thief and return the stolen livestock. In town, Medora buys a rundown inn and transforms it into the Hotel de Morés. Her first act is hiring a new manager, an impressive young woman named Rosie Maddox. When Medora realizes that a cattle rustler might be staying in the hotel, she tasks Rosie with uncovering the evidence.

When the Elkhorn Ranch is invaded by a gang of horse thieves, Theodore Roosevelt and his men put up a valiant fight, but the thieves escape with a string of new horses. An indignant Roosevelt joins up with the Stranglers, a posse of vigilantes led by Granville Stuart who mete out their own brand of frontier justice in the absence of any law enforcement in the Badlands. When they catch up with one of the thieves, Roosevelt learns firsthand that frontier justice isn’t always just. Meanwhile, the business of Elkhorn is thrown into chaos when Merrifield meets with a Chicago beef merchant behind Sewall’s back. Sewall takes matters into his own hands by striking a deal with Medora, an act of defiance that has disastrous consequences. When Wilmot Dow meets the lovely Rosie at the Hotel de Morés, the two youngsters spark an immediate connection.

Now that his cattle operation is up and running at Elkhorn Ranch, Theodore Roosevelt agrees to be photographed by a newspaperman. Determined to look the part, Roosevelt seeks out a seamstress to commission an authentic buckskin suit. While the cantankerous seamstress warns Roosevelt that buckskin isn’t well suited for the Badlands, Roosevelt collapses suddenly with another bout of enteritis, an illness that has plagued him his entire life. Out here on the frontier, without access to the proper medication, it suddenly becomes a matter of life or death. In a race against the clock, his trusted ranch manager, Bill Sewall, rides desperately into the Badlands to find the Sioux village that may have a remedy to save his friend. Meanwhile, the Marquis and Medora find themselves on the brink of financial ruin. To save their business empire, they decide to call in their debts at gunpoint.

Theodore Roosevelt paces the halls of Elkhorn cabin all night, struggling to find the right words. The family of his recently departed wife, Alice, has requested that he write a eulogy in her honor, and this is the first time Roosevelt has had to put words to his unthinkable loss. Sensing the need for a distraction, his partner, Bill Merrifield, suggests a grand hunt in the Bighorn Mountains to bag a bull elk, and Roosevelt leaps at the chance to escape his writer’s block. The arduous journey to Wyoming brings encounters with Cheyenne braves, haunting memories of Alice, and an unexpected dinner with a U.S. Cavalry regiment. When Roosevelt sees a severely wounded soldier who crossed paths with a grizzly bear, he quickly forgets about the bull elk and determines to hunt down the man-eating grizzly before it strikes again.

When a masked bandit terrorizes the stagecoach line, killing a passenger, Theodore Roosevelt and his Elkhorn men join the citizens of Medora to track down the culprit. All the clues point to Redhead Finnegan, a petty criminal and ne’er-do-well who is suddenly flush with cash. The townsfolk confine Finnegan in an abandoned cavalry jailhouse, but he soon escapes and the stagecoach robberies resume. Deadwood’s sheriff arrives to help lay a trap, but things aren’t at all what they seem. In the end, it’s the town’s newspaper publisher who finally puts the clues together and identifies the killer, bringing his reign of terror to an end.

When raging wildfires threaten to consume Elkhorn Ranch, Theodore Roosevelt’s men take quick action to avoid catastrophe, but many cattle perish in the flames. Backed into a financial corner, Roosevelt decides to sell some of his remaining stock to the town’s founder, the Marquis de Morés, before the fall roundup. When the Marquis attempts to take advantage of the situation by making a low offer on Roosevelt’s herd, a prideful Roosevelt walks away from the deal. Soon, other ranchers follow Roosevelt’s lead, and the Marquis retaliates by closing his businesses in town, igniting violence between the area’s ranchers and businessmen. To restore order, the town decides to form a cattlemen’s association. With the ranchers poised to vote for the association’s leader, Roosevelt must decide if he’s truly finished with politics.

Theodore Roosevelt and his Elkhorn men strike out for the open range to participate in their first roundup. The weeks-long undertaking of sorting cattle is a chance for Roosevelt to prove himself a true cowboy. Unfortunately, the changing seasons bring back his asthma, and he is injured in a fall. Undeterred, Roosevelt rides alongside the rest of the cowboys as they drive and sort their herd across the Badlands. But the spirit of adventure quickly turns to fear when one of the cowboys turns up dead. Though it looks like an accident, some of the men aren’t so sure, and the sudden appearance of the Marquis de Morés puts Roosevelt’s mind ill at ease. With the cattle season coming to a close, Dow ponders if he should return to Maine as planned or stay in Medora to build a future with Rosie.

When a lightning strike spooks the herd, an injured Theodore Roosevelt acts quickly to stop a stampede during the fall roundup. Back in town, the annual roundup dance brings the community together, friend and foe alike. What should be a joyful celebration turns ugly when Paddock decides it’s time to settle old scores with the Elkhorn crew. The dance is also Wilmot’s best chance to propose marriage to Rosie, but her heart is torn between a simple life as Wilmot’s wife and a more alluring future as Medora’s protégée. With the Elkhorn ranch secured for the winter under the watchful eye of Merrifield, Roosevelt returns to New York to be reunited with his daughter.