A fire rages on a Western mountain range and, despite the efforts of helicopter crews, firefighters, and Lassie, Ranger Corey Stuart is trapped in the inferno. When a rescue team finally reaches Corey, he is seriously injured.

Severely injured from a raging fire, Ranger Corey Stuart lies in a hospital with Lassie keeping vigil by his side in this conclusion to a two-part series. When Lassie is given to a new Ranger during Corey's recovery, she journeys miles to return to his side.

On a surveying mission of the forest, Scott and Bob are delighted to find wolves restablishing themselves in the area. Then the male is shot while hunting for his pregnant mate and the rangers must save him--and change the hunter's mind about wolves.

Lassie, poisoned by pesticides, is found by an up-and-coming race horse, Glory, and her young owner. Once well again, she befriends a newborn colt on their California thoroughbred farm--then Glory is threatened by a marauding cougar.

Even Hank can't believe all his surgical skills can heal Glory's injured leg, but Monty takes a chance and has her operated on nevertheless after a pep talk from partner Bert. Then it is up to Gary and Lassie to make her well, with exercise and swim therapy.

Ron and Dale return to the Holden Ranch, where Lassie is welcomed by Garth Holden and his foster sons, boys who have been orphaned or abandoned by their families.

While in town picking up a gift for Garth, Ron is knocked unconscious when an earthquake strikes, and when he comes to, Lassie has escaped from the truck. As he and the dog search for each other, Lassie helps fellow animals dislocated by the quake, and Ron enlists his father in the search.

Mike befriends Henry Newton, who flies a Curtis Pusher at airshows under the name ""The Flying Grandpa,"" when his aircraft breaks down in the Holden pasture. His long involved tall tales of bravery during air feats impress the boy, but bother Garth, who thinks Newton's lies might backfire. And when a bear charges Newton and Mike, the elderly man finds out they do.

Garth and Dale survey rangeland for the Forest Service and see a young white stallion challenging the older black leader of a horse herd; Garth predicts the white horse will soon succeed. When he does, driving the injured black stallion away from water, Lassie tries to lead him to safety before he collapses.

As Lassie gently leads the stallion back to the Holden Ranch, Garth and Dale leave food and drink for the animal, hoping he will choose himself to live at the ranch.

Ron and Dale, home from college, go out on the annual stray roundup and make a bet on which of them will find the most cattle. But it's Lassie who gets the jump on them, helps a calf stuck in quicksand, and then must help Ron when he's thrown from his horse.

Garth takes Lassie with him on his visit to Vandenberg Air Force Base, where they meet Jimmy Fredericks, a boy with a weakened leg who has given up believing he will ever walk normally.

After Lucy and Jimmy find Mountie in the cave where Lassie has hidden him, Lucy sends Jimmy for help on her horse. He is frightened to do so, but does so for her sake, and despite being thrown, finds Domenic, the shepherd who shot Mounty. Meanwhile, Lassie returns to the ranch.

When Mountie weakens and then dies, even normally optimistic Lucy cannot understand and sinks into depression, so Sue asks her to help out at the wild animal park to take her mind off her loss. Eventually Lucy begins taking an interest in the animals, including a llama about to give birth.

A runaway inner-city orphan is taken in at the ranch, but is distrustful of everyone.