A small-town editor and a big-city reporter investigate a wealthy rancher's mysterious death.

At the Flying T Ranch in Oklahoma, home to a prized herd of Hereford cattle, Jan Holloway, the niece of late owner Sam Talbot, awaits the reading of her uncle's will while Duke Lowery, the twelve-year old ward of ranch foreman Gabby Whittaker, nurses his pet calf, Ricky. In the nearby town of Hereford Heaven, meanwhile, newspaper reporter Connie Edwards arrives from St. Louis and meets Roy Rogers, the editor of the local paper. Connie has come to write a story about the Herefords, and so Roy escorts her to the Flying T. They arrive just in time to learn that Sam has bequeathed the ranch to Duke and has left Jan only a $5,000 stipend. Jan's foreman, Steve McClory, who had anticipated Jan's inheritance of the Flying T, angrily accuses Gabby of manipulating Sam and threatens to contest the will. Sam has bequeathed Roy a prayer book, and when Roy opens the book, he finds a message from Sam, asking him to investigate the circumstances of his death. Against Roy's wishes, Connie phones in the story of foul play to her newspaper in St. Louis. Furious when the story is published, Steve plots to eliminate Duke before the will can be probated. Later that night, gunshots are fired at Duke's bedroom window. Roy pursues the boy's assailants, and shoots one, but the other escapes. When Connie refuses to divulge the source of her story, Sheriff Barclay jails her for refusing to cooperate. The next morning, Roy posts her bail so that she can attend the town's Tuesday morning Breakfast Club meeting. During the meeting, Roy realizes that Sam was killed on a Tuesday morning on his way to the event, and decides to let Sam's horse retrace his footsteps from the day of the murder. As he approaches the creek, the horse rears up and bolts. Searching the area, Connie and Roy finds Sam's watch in the creek, stopped at 9:17. From Devoria Lassiter, Sam's housekeeper, Roy discovers that on the day of Sam's death, his horse arrived back at the ranch just as the 8:45 train whistle blew, implying that the horse came home before Sam was killed. Deciding to question Judnick, the coroner, about Sam's death, Connie and Roy proceed to his office. As Roy starts to rifle through the files, Jud appears, gun in hand, and a fight ensues. After overpowering Jud, Roy threatens to exhume Sam's body. Spotting Roy through the window, Jan waits until he leaves and then enters the office to confer with Jud, her accomplice in Sam's murder. At the ranch, meanwhile, Ricky falls ill and Duke, fearing that the calf will have to be destroyed, runs away with his pet to the cave at Rainbow Falls. Finding them there, Devoria treats Ricky with an herbal cure. As Roy and Gabby search for the missing boy, they meet Devoria along the trail and she directs them to Duke's hideout. At the falls, meanwhile, Duke witnesses a meeting between Jan, Jud and Steve. After Steve shoots Jud in the back, Jan notices Duke hiding in the bushes and pursues the boy. To elude her, Duke plunges into the falls. Spotting Roy and Gabby approaching in the distance, Steve and Jan mount their horses and gallop off to Jan's ranch. When Duke tells Roy that Steve shot Jud, Roy races toward Jan's. Jan has rallied her cowhands to fend off Roy's attack, but with the help of Gabby and the Sons of the Pioneers, Roy routs her men. Now cornered, Steve and Jan quarrel, and after shooting Jan, Steve speeds away in his car to catch the 8:45 train. After confessing that she killed Sam in order to inherit the ranch, Jan dies in Roy's arms. Jumping onto his horse, Roy races to the train and during a daring fight atop the freight cars, apprehends Steve. All ends happily as Ricky recovers and Connie, Roy and Gabby ride off into the sunset singing.