In the late 1890s, on a California mountain ranch owned by the Bridges family, old Joe Sam, a former Piute chief who works as ranchhand, alerts the eldest son, Arthur, that their nemesis, a black “painter,” or mountain lion, has returned with the first snow and is killing off livestock. As the gentle Art and his domineering brother Curtis prepare to track down the cat, the rest of the family awakens at daybreak. At breakfast, Curt, who has been running the ranch for the family, bullies his siblings, including spinster Grace and their youngest brother Harold, called “Hal.” Curt takes perverse pleasure in baiting Hal’s visiting girl friend, Gwendolyn Williams. Ma Bridges, their bitter, Bible-quoting mother who dotes on Curt, feels threatened by Gwen and demands to know Hal’s intentions, reminding him that he cannot support a wife. Art, the peacemaker of the family, suggests that Curt, who has maintained tight control over ranch affairs, give Hal a share of the ranch and that the family hold an old-fashioned house-raising, so Hal can be free to start his own family. Art petitions Pa for support, but the older man, a former scholar who has become an alcoholic, says he has not had a say in ranch matters for years. Although Gwen is able to confront Curt while fending off Ma’s coldness and Pa's amorous attention, she is frustrated that Hal refuses to stand up to Curt in her defense. After Art and Curt leave, Hal explains to Gwen that Joe Sam first saw the mountain lion years ago, after it killed the last of his family. Hal says he usually carves a wooden figure of the animal for the superstitious Joe Sam, who believes it keeps them safe, but the snow, along with the cat, came before the carving was finished. Meanwhile, as they trail the cat, Art again tries to speak on Hal’s behalf, but Curt refuses to listen. Realizing that the cat has gotten away, Curt returns home alone to get snowshoes and food, so they can continue to track it in the mountains. After Curt leaves, the cat returns and kills Art, and at the ranch, Joe Sam senses what has happened. When Curt shows up for supplies, he again harasses the weaker members of the family and, before leaving, blames the mountain lion, which he claims to be the evil in everybody, for the trouble in the world. Back on the trail, Curt finds his brother’s body and ties it to his horse, but the horse shies from the smell of blood on Art’s cowskin coat. After exchanging his bright red coat for Art’s, he sends the horse home, vowing to kill the mountain lion. When the horse bearing Art arrives at the ranch, Ma lays her son out, admitting to Hal that she and Curt fought Art, who defended the rest of the family. Later, Ma sees Hal and Gwen kissing, and orders Gwen off the ranch, but Pa drunkenly accuses Ma of withholding love. Hal prepares to leave with Gwen, but Ma manipulates him into staying to see to Art’s burial. Frustrated that Hal never stands up for himself, Gwen decides to make the trip home alone, until Hal, for once taking control, orders her to wait until he has finished. Meanwhile, Curt takes refuge in a cave for the night, but finds that the food he brought from home is in the coat he sent back with Art. In Art’s coat pocket, he finds a book of John Keats’s poems and panics when he reads the line, “When I have fears that I may cease to be….” The next day, at the family's simple graveside ceremony, Ma grieves about the things she should have said when Art was alive. Later, as Hal again prepares to leave with Gwen, Ma orders Hal to build a great bonfire to show Curt the way home. Pulling Hal aside, Grace warns him to escape while he can, but, as Ma expects, Hal stays. Meanwhile, Curt, who is still stalking the cat, tries to build a fire. With his last match, he sets fire to Art’s book, but falling snow from a nearby tree puts it out. Thinking he sees a bonfire in the distance, the now irrational Curt runs toward it and falls to his death over a cliff. After three days, despite the peace Curt’s absence brings, Hal and Joe Sam set out to look for him. Mourning that Curt will die with her sin on his soul, Ma recalls that Pa did not want to leave civilization and that all of them, especially Grace, have suffered because of her insistence. On the trail, after Joe Sam finds Curt’s trail leading over the cliff, the cat suddenly appears and Hal shoots it. Joe Sam then announces that there will be no more trouble, because Hal is now the head of the family. Hal and Joe Sam return home, and as they approach the farmhouse, they see the family, now united, working together to keep the bonfire burning.