John Chandler, Alan Ladd, a former Confederate soldier, arrives in an Illinois town with his 10-year-old son, David Chandler, David Ladd, to see Dr. Enos Davis, Cecil Kellaway, who recommends an operation by a doctor he knows in Minnesota. The boy has lived mute since witnessing his mother burned to death when Union soldiers torched their homestead, and he has not spoken a word since that tragedy.
In the street outside Dr. Davis' office, Chandler tells his expert sheepdog, Lance, King, to clear the road of a flock being herded through town. The sheep belong to rancher Harry Burleigh Dean Jagger and his sons, Jeb Harry Dean Stanton and Tom Tom Pittman; trained dogs are extremely valuable, and the Burleighs try to steal the flock. Chandler fights them while a passing Linnett Moore, Olivia de Havilland, keeps David safe and out of the way. Harry knocks Chandler out, pours whiskey on him, and then reports to the sheriff that he was attacked by a drunk.
Chandler must pay $30 or serve 30 days in jail. Linnett intervenes, offering to let him work off the debt on her farm and, in addition, to cover the fine so that he can be released. Chandler, initially reluctant, is won over by her decency. As they spend time together, he learns that Linnett is being pressured by the stubborn Burleighs to sell her land, which blocks the easy passage of his sheep to pasture and to the railroad. Over time, Chandler and Linnett grow closer, even though he is determined to keep his distance, knowing they will soon leave the town.
A Minnesota trip for treatment is expensive, but Chandler resists offers to take Lance, since David loves the dog. Ultimately, he decides to sell Lance after all, for a high price, to finance the trip and the operation. He asks Linnett to accompany David north while he harvests her crops and rebuilds the barn burned by the Burleighs’ men in a bid to pressure Linnett to sell.
The operation does not work. When they return, David is devastated to find Lance gone. The dog is acquired by the Burleighs to pressure Chandler and Linnett. When Chandler goes to their farm to try to buy the dog back, Harry Burleigh tells him he can have the dog as a gift, but has already instructed his two sons to help murder him, as an apparent thief. David arrives at the moment gunshots erupt, and it becomes clear that the Burleighs do not intend to let his father leave. Seeing one of the sons rising to shoot from a hidden spot, David shouts a warning to his father. Hearing it, Chandler is able to pivot and shoot that son first, then Burleigh. The other son lowers his rifle instead of firing. Chandler walks back with David and Lance, guiding his horse toward Linnett’s farm, as David begins to re-learn how to speak.
