Bart arrives in St. Louis to find his missing cousin Beauregard "Beau" Maverick. The last place left to find Beau is at the docks, a place so dangerous the driver refuses to take him there. As Bart disembarks, he sees Sheriff Muldoon taking care of some troublemakers and asks for his help finding Beau. The gambler explains that he hasn't seen Beau in five years because his cousin has been in England, and Muldoon suggests that if he's looking for an Englishman, he go see the Honorable Freddie Bognor at the Blue Moose Saloon.
Taking Muldoon's advice, Bart arrives at the Blue Moose and quickly spots Freddie, sporting a monocle, accompanied by two hired bodyguards, , and beating everyone at poker. When he sees Bart watching him, Freddie sends one of his bodyguards over to bump in to Bart and lift his wallet, but Bart catches him at it and a fight breaks out. Bart crawls under the table with Freddie as they both take refuge, and the two men make a hasty escape. Once they find a quiet spot to talk, Bart explains that he is looking for Beau. Freddie has no idea where he is, but he tells Bart that he has a $2,000 idea and invites Bart to dinner. He explains that his father, the Marquis of Bognor, received a prospectus from the Bar H, a training ranch for dudes located in Montana. Freddie has no interest in going there and doing anything resembling labor, but he offers to pay Bart $2,000 to take his place. Bart isn't interested and Freddie accepts his refusal... and steals his wallet.
Outside, Bart finally locates Beau, who is talking to reporters about how he received a medal for heroism. Bart gets his cousin alone and tells him to quit spreading stories about his heroic deeds, and points out that Pappy exiled Beau to England so his heroism wouldn't ruin the Maverick family reputation. Beau explains that he won the medal for the inadvertent capture of a Confederate general after he distracted the man by beating him at poker, allowing Union troops to capture him. He then explains that he was arrested when Freddie stole the purser's trunk on the ship from England and left beau to take the blame. Bart gets an idea and says that he knows a way that they can make $2,000. Beau agrees to hear Freddie out but asks for $5 first to get his bags out of impound. Bart discovers that Freddie stole his wallet.
Beau and Bart track Freddie down to a hotel where he's playing a private game of poker. When he spots them watching, he drops the cards and an argument breaks out over whether to declare a new hand. Freddie grabs the pot and slips out, but the cousins stop him and recover Bart's wallet. Beau offers to take Freddie's place at the Bar H, but insists on another $1,000 to pay his bond and another $1,000 for having to take the blame for Freddie's theft. Freddie has no choice but to accept and gives Beau his signet ring and identification papers. Once Freddie leaves, Bart promises to tell Pappy that Beau is a poker-playing scoundrel after all, and they discover that Freddie has stolen Beau's pocket watch.
Beau takes the stage to Montana, but two masked men order the driver to pull over. However, rather than rob it, they take ask which one of the passengers is Freddie. When Beau identifies himself as the Englishman, they take him away and send the stage on its way. The two thugs, Pecos and Brazos, take Beau to a cabin where an Irishman named Herbert is drinking heavily. He's working with Molly, an English waitress, who knows the Marquis of Bognor from when he drank at the Soho tavern where she worked. Herbert plans to demand a ransom for "Freddie" and get the Marquis to pay 20,000 pounds for the return of his son. Molly admits that she's never seen the Marquis' son, but confirms that the signet ring that Beau is wearing belongs to Freddie. Beau claims that he's a wanderer named Courtney Faversham, and that he won the signet ring from Freddie in a poker game. Pecos and Brazos assure Herbert that Freddie's name was on the stage's passenger list, and Herbert, a former barber, prepares to cut Beau's throat with his trusty razor rather than leave a witness alive. Beau immediately admits that he's Freddie, showing them the Englishman's credentials. He then starts helping Herbert write the ransom note, asking for an additional 5,000 pounds to cover Beau's "consulting fee." Beau, clearly an expert on ransom notes, impresses Herbert. He then says that they need to send it to the Marquis' business partner in St. Louis: Bart.
In St. Louis, Bart is in a private poker game sitting on a winning hand. A clerk brings in Beau's note and Bart has no choice but to leave. He writes to the Marquis suggesting that he send the 25,000 pounds but that they'll put it in a bank. When the kidnappers come to get it, they'll arrest the men and rescue "Freddie."
Back in Montana, Beau spends the spare time playing poker and taking Herbert for everything he has. Herbert finally sends Beau away, warning that if they don't have the money in five days, he'll finish him off. Outside, Molly approaches beau and tells him not to push Herbert too far. She explains that the training ranch is just a normal cattle ranch, run by a man named McGee, and that Herbert sent a fake prospectus to the Marquis in the hopes of luring Freddie there so they could kidnap him. Pecos and Brazos got jobs at the ranch and intercept the mail that the Marquis has sent there to confirm it's a training ranch. Molly, who is in love with the Marquis, is having second thoughts about the kidnapping scheme. Beau suggests that she can buy a boat back to England with the ransom money, but Molly warns him that the Marquis will never pay to get his gadabout son back.
In St. Louis, Bart is winning another hand of poker when he gets a telegram from the Marquis. Again he's forced to quit the game, and learns that the Marquis is coming to the U.S. in person to recover his son rather than pay the kidnappers. Bart goes to Freddie and explains the situation, and suggests that Freddie keep a low profile rather than let his father discover that Freddie tried to weasel out of going to the ranch. He sends Freddie to what he claims is a cruise ship, the Cynthia B, and Freddie quickly agrees. However, when he gets there he discovers that Captain Wolf Kratkovich owes Bart money and is going to put Freddie to work as a crewman.
Bart greets the Marquis when he arrives, and he insists on going to Montana to rescue his son and deal with the kidnappers himself. Bart has no choice but to go along and the two men make their way across the countryside.
When the five days are up, Herbert and Pecos go to the Inscription Rock, where Bart was told to drop off the money. Molly and Beau worry that Bart will get there in time, and Beau wonders why Molly stays with Herbert. When she admits that she has nowhere else to go, Beau points out that the Marquis must have had feelings for her since he kept visiting her at the tavern in Soho, and he promises that he'll have his "father" take Molly back to England if she helps him. Molly agrees and Beau tells her to throw a bottle of Herbert's rotgut whiskey into the fireplace when the time is right.
Herbert and Pecos make sure that the money hasn't been dropped off, and spot Bart and the Marquis riding to the Bar H. Pecos rides to the Bar H while Herbert goes back to the cabin to dispose of Beau. When Bart and the Marquis arrive at the ranch, the Marquis immediately gets into an argument with McGee. When the foreman attacks him, the Marquis knocks him to the ground with one punch, winning the man's admiration at his boxing technique. As the two men chat, Pecos watches the exchange and stumbles over some firewood. He tries to casually walk away but Bart figures that something is going on. McGee explains that Pecos and his friend Brazos showed up and asked to run the herd up at Inscription Rock, and Bart decides to ride after Pecos. He realizes that he's being followed and gallops off, and Bart goes after him. McGee and the Marquis suspect that Bart is having a fit and ride off after him to bring him back and get him treatment.
Back at the cabin, Herbert prepares to kill Beau, who asks for a last look out the window for his dying request. While Beau stalls, he tells Molly to get the whiskey bottle. However, Pecos comes in and Bart comes in after him, and Bart tries to get Beau out of trouble by telling Herbert who his cousin really is. When Molly realizes that Beau lied to her about being able to put in a good word for her with the Marquis, she blurts out their escape plan. Herbert locks her in the back room and has Brazos tie up Bart and Beau. The three crooks spot the Marquis and McGee approaching and go out to ambush them, but Herbert leaves his razor on the table. The Mavericks spot it and hobble to get it.
As Herbert prepares the ambush, he realizes that he left his razor behind. He goes to get it and sees the Mavericks, apparently still tied up. As soon as he turns to go, they jump him and a fight breaks out. Bart struggles with Herbert while Beau goes after Pecos and Brazos. He manages to knock out Brazos, grab his gun, and kill Pecos. Inside the cabin, Bart and Herbert knock over the stove and then knock the bottle of whiskey onto the hot coals. The alcohol bursts into flames and Herbert runs out, but Beau makes short work of him with an assist from Bart. The Marquis and McGee come charging up, and Beau suggests that they let the Marquis rescue Molly. He charges into the smoke-filled cabin, rescues the woman, and immediately falls back in love with her.
Later, the Marquis and Molly are quickly married and promise the Mavericks that once they tidy up affairs in England, they'll return to raise longhorns at the Bar H. There's still the matter of Freddie, and Bart assures the Marquis that his son is getting a workout with Kratkovich, the toughest riverboat man on the Mississippi. The Marquis gives each Maverick a thousand pounds for their help and departs by boat. As Beau and Bart go to get dinner, they bump into Kratkovich... who is now working for Freddie, the new owner of the Cynthia B.