Lassie and drifter Mark come upon a fire on the Pearson ranch, putting it out for which the Pearsons are grateful. Their collie Duke bonds with Lassie so Mark parts ways with his traveling companion. The dogs later tangle with a vicious stray.

Lassie finds happiness with Sgt. Hayes learning to herd sheep on his ranch. She has three pups with his collie Duke but the sergeant is under the mistaken belief a killer wild dog is the father. Lassie runs away to save her puppies.

After Lassie leaves the Hayes Ranch she finds shelter in a small cave with her pups but has no food or water. A young mute boy Kerry finds them, bringing them food but learns he is to be sent away to school. He then runs away.

The Holts and their friends search for the runaway Kerry but he is with Lassie and her pups. After a dangerous encounter with a mountain lion Kerry is found. Lassie leaves one of her offspring before continuing her journey.

Lassie's journey goes on, teaching the two pups about predators and survival in the wild. Taking shelter in an abandoned building during a storm, the adventuresome youngsters still find danger but Lassie keeps them safe.

Lassie and her pups meet Davey Braddock, a boy so grief-stricken by the recent death of his dog that he doesn't want anything to do with any other dog. Lassie and her pups have their work cut out for them.

Lassie and her remaining puppy meet a young teen Jodi Tyler in the forest. Living there with just her father, she has a special bond with animals. Lassie helps in a bulldozer accident then leaves her pup before continuing her journey.

Lassie befriends an elderly man who feeds a flock of birds and claims that they love him. His friends laugh at him about this claim, but when he becomes ill the behavior of the birds surprises everyone.

After a forest fire caused by a carelessly discarded cigarette, Lassie assist various animals recover from difficulties caused by the fire.

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Lassie's journey is interrupted when she is sickened by insecticide. Found by Gary and his father, the collie regains her health on their horse ranch. She calms a nervous stallion, helps deliver a colt and fights a cougar.

Gary is upset over Glory's cougar injury and Lassie tries to comfort him. Bert is convinced to give equine surgery a chance so they follow the horse through the operation and swim therapy until he's ready to return to the track.

During a storm Lassie takes shelter in a garage belonging to a lonely woman whose children have all gone. Lassie is dirty so the woman doesn't want to let her come into the house. Then the loose dirt behind her house begins to slide.

Lassie brings together two lonely people when she finds an injured bird and brings it to a man. He enlists the help of his neighbor, a single woman. While caring for the bird, they learn to care for each other.

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Lassie makes her way upstream after helping rescue two campers who left their father to try out a new raft and were swept downstream on the rapids. Once she finds help, however, she must find the boys, who are also heading upstream. With Robert Patten, Don Eitner, Scott Perry, Robert Ferrel, and Danny Madrid. Note: When the question of who Lassie belongs to arises, the forest ranger replies, "Oh, I guess to everyone who needs her."

A rural boy, bored with his surroundings, decides to strike out on his own and go exploring. Being angry with his neighbor for posting "no trespassing" signs makes it easier for him to steal that neighbor's horse for the journey. .

When Patty comes to visit her aunt, she is poisoned by arsenic in the water. Her aunt finds the source of the poison in an old mine but is trapped when the floor collapses. Lassie helps the aunt by finding Patty before she leaves for home.

Lassie makes new friends at the beach, mixed breed Skipper plus two surfers, new acquintances Reed and John. Reed is with the harbor patrol but John is aimless, who "borrows" a boat. Lassie must save John after an accident.

Lassie returns to the Braddock ranch where she left one of her pups. While playing Lassie falls down an abandoned well. The Braddocks begin to dig to get the heroic collie out and but are needing help.

As Lassie remains trapped in the well the people she met and helped the previous months converge. In between frequent flashbacks everyone works diligently, including a honeymooning couple, to rescue the beloved dog.

Lassie finds an abandoned grey kitten and protects it throughout a memorable day. The cat finds a lake to fall into, a hungry owl, and a beligerent pig. Lassie manages to find a new home for the wayward youngster.