Not long after the Civil War comes to a close, a young family finds their home in the vibrant community of Salt Licks, Texas. Jim Coates (Fess Parker), along with his wife Katie (Dorothy McGuire) and their two sons, Travis (Tommy Kirk) and Arliss (Kevin Corcoran), aim to build a fresh life, but financial struggles plague them. The family manages only a small sum of worthless Confederate money, a situation shared by the other families around them. Seeking a way out, Jim partners with fellow ranchers for a cattle drive to Kansas, hoping to sell their livestock and return with the resources they desperately need.
As Jim prepares to leave for 3-4 months, he turns to Travis and expresses his reliance on him to help his mother and tend their ranch during his absence. Jim promises to bring back the horse Travis longs for, inspiring the boy to take his duties seriously. One day, while plowing the cornfield with Jumper the mule, Travis' routine is abruptly disrupted when a big yellow dog leaps into the fray, chasing a rabbit. The excited mule bolts, dragging Travis behind before he manages to free himself. Angered by the dog, Travis hurls rocks, threatening to shoot it if it returns.
Meanwhile, Arliss is intrigued by the dog and, despite their mother's disapproval of him catching small animals, he becomes determined to adopt it. When the dog appears at their doorstep the following morning, tensions rise between the brothers as Arliss defends his newfound friend, ultimately convincing their mother to allow the dog to stay. Thus, Yeller becomes a part of their family.
At first, Travis remains indifferent towards Yeller, but his perspective shifts after bringing home a deer, cautioning the dog not to touch the meat. Contrary to Travis' expectations, the dog showcases remarkable obedience, which impresses Travis enough to accept Yeller into their lives. Arliss joyfully takes to Yeller, treating him as a companion for fishing, swimming, and even attempting to catch a small bear cub. During a tense encounter, Yeller defends Arliss from a mother bear, further solidifying his place in the family and earning Travis' admiration.
Visitors to the Coates home, such as Bud Searcy (Jeff York) and his daughter Elizabeth (Beverly Washburn), add a sprinkle of humor to their lives. Bud, a lazy man left behind while the community's men are in Kansas, delights in storytelling and relies on his daughter for chores. Secretly, Elizabeth shares with Travis that she's spotted Yeller stealing food but remains quiet to protect him, his pups expected soon.
To prevent trouble, Travis puts Yeller on guard duty in the cornfield—a plan that proves effective. Their humble milk cow, Rose, soon seeks solitude to give birth, but she attacks when Travis approaches. In a heroic moment, Yeller intervenes, showcasing his loyalty once again. However, when a passing rancher, Burn Sanderson, identifies Yeller as his missing cattle dog, Travis faces a moral dilemma. Though initially reluctant, he ultimately lets Yeller go for a horned frog and a home-cooked meal, as a means of ensuring the dog belongs to them.
As the days progress, frightening signs of hydrophobia emerge in the area, leading to tensions in the Coates household. When symptoms appear in Rose, a tragedy unfolds, and to protect them all, Travis is forced to confront the painful reality of losing Yeller as well. After a battle with an aggressive wolf where Yeller demonstrates his courage, it becomes apparent that he too may be infected. As Yeller changes, showing aggression, Travis grapples with overwhelming emotions, leading to a heart-wrenching decision he never wanted to make.
Following Yeller’s passing, Mr. Coates returns home, bearing gifts but finding his son disillusioned and grief-stricken. Understanding the gravity of Travis's heartache, Mr. Coates imparts wisdom on the balance of life—the inevitability of both joy and sorrow. As Travis observes a puppy reflecting Yeller's spirit, he realizes his father’s insight. This bittersweet moment restores a flicker of hope in Travis as he recognizes the connection between life’s cycles and the enduring nature of love and memory.
