A young rancher named Jayce Frederick stands to inherit his late father's ranch. However, because of money problems, the bank is foreclosing on the farm and all his livestock. His very beautiful young fiancé, Kathy, believes that one horse in particular, a black Callabero she just can't seem to rope, is what they need to start over. So, with $500 in hand, Jayce agrees to ride to auction barn in Rimville to buy back the horse
While crossing the Ponderosa where the Cartwrights are in the middle of a logging harvest, Jayce is injured in a blast. Ben takes the injured young man to the logging headquarters where he pleads with the Cartwrights to go to auction and bid on the horse. Little Joe and Candy agree to act as his proxy.
Bidding against a man named Rio, and enduring the auction attendees' amusement at the Callabero's wild demeanor, Joe submits the winning bid of $300. Joe and Candy collect the bill of sale, have a beer at the local saloon (enduring a woman's deep depression over a horrible song played on the Victrola) and figure that's that.
That's when trouble begins for the Cartwrights. Gabriel Bingham, Jayce's rich uncle who took over operation of the ranch after his father became crippled, is a ruthless, avaricious man who wants that horse and will stop at nothing to get it.
First, he attempts to buy the horse from Joe at the saloon for $600, but both he and Candy refuse. The sheriff, who also happens to be the bartender and a witness to the failed offer, is no help.
Joe, and later Candy, find themselves having to explain to Kathy (in vain) that they were buying the black horse for her boyfriend. Fortunately, she believes them.
Later, Rio, Bingham's top lackey, and his other goons knock Candy out in the stable where the horse is being kept, and swipe the bill of sale. Knowing he is next in line to inherit the ranch if Jayce dies, Bingham orders his gang to bring him Jayce, dead or alive.
Bingham's gang find Jayce, with his nephew about to lose a shoot out, when Joe (and the other Cartwrights) show up to even the odds. Ben then asks Jayce to explain what's going on, particularly since one of Bingham's henchmen was killed in the line of fire. He learns Bingham was supposed to teach Jayce the finer art of ranch management but had given him only menial tasks. In the meantime, Bingham refused to pay his nephew, knowing that monetary problems could result in foreclosure and allow Bingham the opportunity to buy the ranch outright. So he took $500 from Bingham's safe (part of the back wages he was owed) to buy some of his livestock back, advising that his uncle will try to portray the incident as a theft.
Candy gets the horse back and brings it to the ranch, where he is again outnumbered and restrained.
Ben, Hoss and Little Joe track down Bingham and demand an explanation, which he tries to explain in his favor. Meanwhile, Jayce and Kathy show up to claim their horse and another gunfight begins. The Cartwrights again quickly even the odds, but Bingham sneaks unnoticed to Jayce's hiding place beneath a wagon. Just before Bingham is about to get a clear shot at his nephew, Candy barges out of the stable and is able to defeat Bingham. As a grateful Jayce and Kathy celebrate and thank the Cartwrights, a disgusted Ben tells Bingham as he's being led off, "I understand you a whole lot better now."