On Punta Libre outside of Miradero, the young foal Governor and his mother are attacked by an unseen creature. Meanwhile, Lucky and Pru race home on horseback to assist with Aunt Cora's tea party, where she is inducted into the Daughters of Miradero Aid Society. Cora's guests plan a horseback ride, and the PALs do nothing to dispel the impression that Cora is an expert rider, though in reality, she has not ridden a horse but once as a child. The PALs give Cora some lessons in the ramada, then head out for a ride in the wilderness, where, just as a storm approaches, they discover claw marks on a tree trunk, which Pru identifies as belonging to a mountain lion. Back at the ramada, just as Cora has decided she has had enough horseback riding for one lifetime, Mr. Granger delivers an injured Governor and the news that Governor's mother did not survive the mountain lion attack. Lucky sends Spirit to check on his herd. Al and Cora then forbid the PALs to go horse-riding until the lion leave Miradero.
Inside the Prescott house, as an electrical storm brews outside, Cora introduces Lucky to the Prescott family quilt, but Lucky worries for Spirit, and determines to sneak out, announcing, as a pretense for her absence, that she will be taking a hot bath upstairs. She puts the goose Clancy in the filled bathtub and descends from the window, then takes the horse Sagebrush from the barn and makes her way across the frontier.
Spirit tries to shelter his herd under a rock, but they bolt, and cross paths with Lucky, as the mountain lion attacks Spirit. The sound of thunder startles Sagebrush, who throws Lucky, panics, and bolts away, leaving Lucky in the wilderness with the storm coming. Lucky hears Spirit neigh and ventures on.
Meanwhile, Aunt Cora discovers Clancy enjoying the tub, and that Lucky has broken curfew and sneaked out. She takes a lantern to the barn and one after one decides against all of the stabled horses, but then her face lights up as she sees what must be a suitable ride.
Having found Spirit injured, Lucky realizes the mountain lion is still nearby, and still a threat to them both. She tries to make use of the advice given her by Mr. Granger, to stand her ground and make herself seem threatening, but even throwing rocks at the mountain lion cannot compel it to desist. Just as it seems ready to attack, two shotgun blasts ring out in the night, scaring the mountain lion away. Aunt Cora arrives, riding Señor Carrots side-saddle, and carrying the lantern and shotgun. She chides Lucky for running off, but helps her get Spirit to his feet to make the long walk back to Miradero.
Exhausted, Spirit collapses just outside of town, near the Prescott house. Lucky runs to find Mr. Granger and get help. Seeing that Spirit is shivering and in shock, Aunt Cora retrieves the family quilt to cover Spirit until Pru and Mr. Granger can arrive with a sledge dragged by Chica Linda. Spirit and Governor recover in the barn, with Lucky, and even Aunt Cora, keeping close watch.
Notes & trivia
- The "lion" of the title could refer literally to the mountain lion Lucky faces, or figuratively to Aunt Cora, the "lion of the family" whose mettle saves the day.
- This is the first time any building in Miradero is shown to have indoor plumbing with running water.
- The fight between Spirit and the mountain lion is probably a callback to Spirit: Stallion of the Cimarron, where the original Spirit fought, and defeated, a mountain lion preying on the coals of his herd.
- The scene where Spirit tries to flatten the mountain lion under his back is similar to how the original Spirit defeated the mountain lion.