George Montgomery, Diane Brewster, Edgar Buchanan, Emile Meyer, Jerry Hartleben, Bryon Foulger, Denver Pyle. After capturing a wild stallion for a local cattle baron, a young boy decides he wants to keep the horse for himself, causing problems for his mother who desperately needs the reward money

In the cattle country near Piute, widow Martha Morse is struggling to save her small ranch, despite the machinations of wealthy rancher Matt McGuire, who wants her to sell it to him. After stealing cattle from her herd and preventing the bank from loaning her money, he pressures real estate agent A. B. Orcutt to deny her a $500 loan to maintain badly needed government grazing rights for her cattle. Her ranchhand, Randy Burke, and his friend Idaho help Martha as much as they can, and Randy, who is in love with Martha, proposes. Martha is reluctant to accept, even though she loves Randy, because she does not want to burden him with her troubles, but agrees to marry him on the same day that the notorious black stallion "Lightning" is spotted in the hills by Martha's son Bucky. While Bucky wants to capture the horse to keep for himself, Doc Weber and Woody Barnes, two of McGuire's hands, want Lightning for the $500 reward he is offering for its capture. Although Randy and Idaho warn Bucky that capturing a wild horse is too dangerous for a boy, Bucky refuses to give up. The next day, Randy and Idaho go to Piute to help Martha. Because neither can raise any money or find out about the missing cattle, Randy tells Idaho that their only hope is to capture Lightning for McGuire's reward. Unknown to them, Doc and Woody have overheard their conversation and follow them out of town. In the hills, none of the four men is able to capture Lightning. Woody is able to rope the stallion, but Lightning tugs so hard at the rope that he pulls Woody's saddle off, forcing him to the ground. Following altercations between Randy and Doc and Woody, McGuire's men want revenge. Unknown to the adults, Bucky, who has also been tracking Lightning, finds him trapped in a canyon, after Woody's rope and empty saddle ensnarled him by a tree. With help from his dog Buzz, Bucky is able to secure Lightning's rope to the tree, then rides back home. At dinner, when Bucky wonders out loud how a person might tame a wild horse, Randy and Idaho explain how it might be done, beginning with depriving the horse of sleep, but again warn him not to try capturing Lightning. Later, after seeing Martha crying from exhaustion and worry over the ranch, Randy tells her that he has a plan to get the $500 before the deadline on Saturday, at 12:17 p.m. Meanwhile, Bucky and Buzz go out to the canyon to see Lightning, and Bucky orders Buzz to stay and keep Lightning awake. Late that night, Randy and Idaho ride into town and Randy walks into Orcutt's office, which is closed. While Woody secretly peers through the window, Randy demands that Orcutt give him $500 from the safe. The sympathetic Orcutt tries to talk him out of it, saying he will not press charges if Randy simply leaves, but Randy is firm. After Orcutt gives him the money, Randy insists that he take a note for it, but Orcutt says that this is coercion and theft, not a proper loan. Randy then insists that Orcutt press charges and goes with him to the office of Sheriff Cap Fellows. Orcutt says that Randy robbed him at gunpoint, but when Randy shows him the note and Idaho, who has been visiting Cap, hands him his gun, proving that Randy was unarmed, Cap concludes that the $500 is a proper loan. After Orcutt leaves, Randy tells Cap that Orcutt needed an excuse to give Martha the money without angering McGuire, and this was the only way. Riding back to the ranch, Idaho suggests that Randy ride ahead and he will lag behind, in case of trouble. Unknown to them, Woody has reported what happened at Orcutt's office to McGuire and the two men pull a rope across the trail. In order to avoid Doc, who has been chasing him, Randy is riding so fast that his horse trips on the rope, causing Randy to fall to the ground. While Randy is unconscious, McGuire steals the $500 and rides off after shooting at the fast approaching Idaho. Later, in Cap's office, the town doctor dresses Idaho's wounded arm and sends him and Randy home. After they leave, Orcutt tells Cap that he keeps a list of serial numbers of all bills that come through his office. On Saturday morning, Martha, Idaho and Randy are despondent that she is about to lose her grazing rights. At breakfast, they explain the situation to Bucky, who had not previously known about McGuire's $500 reward offer. Knowing that he must give Lightning up to save his mother's ranch, Bucky confesses that he has Lightning, who has become more docile. Martha, Randy and Idaho then follow him out to the canyon. Although Randy, too, does not want to hand Lightning over to McGuire, he takes the final step of riding Lightning until he is broken. Meanwhile, McGuire is waiting in the government office in town and tries to pressure the clerk to take his money to pay for the rights to Martha's grazing land, but the clerk is adamant that the leases do not expire until 12:17. At 12:15, just after McGuire convinces the clerk to start filling out the papers, Randy walks in and tells McGuire that Lightning is outside and he is claiming the $500 reward to renew Martha's lease. When McGuire says he will pay after taking out the lease himself, the two draw their guns, then start a fistfight after the clerk draws his gun to prevent a killing. During the fight, which spills out onto the street, Woody sees McGuire's abandoned gun and throws it to him, but Idaho shoots it out of McGuire's hand. When Cap arrives, the clerk tells him that McGuire started the melee and says that the lease money is inside. Cap then looks at the bills McGuire was using, compares the serial numbers to Orcutt's list and arrests McGuire. Now able to renew the lease, Randy tells Bucky that Lightning is his and they happily ride back to the ranch.