Ron reads a letter to the boys that Garth will remain a VISTA volunteer and his brother Keith will take charge of the ranch. This upsets the boys and Mikey takes off with Lassie. A storm related fire endangers Lassie but Keith proves himself.
Lassie and Lucy eagerly anticipate the return of the doves to the local mission. While waiting they wander the town, greeting people and then help the gardener Johann. A hawk threatens the first dove they see.
A storm knocks down a fence allowing a foal to wander off and injuring the mother. Lassie and Lucy leave on horseback to search for the colt followed by Ron and Dale. A tumble into a river endangers the young animal.
Crows are marauding the corn and Lassie can't fend them off herself. The boys create a scarecrow but the birds aren't impressed. One steals Mike's $3 and he falls into a water storage tower trying to get it back. Lassie must rescue him.
Lassie finds a hearing impaired boy, who cannot speak, so she lets Keith and Dale know. They bring young Lucy over to communicate with him but he won't identify himself. The boy then finds an injured dog that he bonds with.
The mystery boy turns out to be Tommy, who is a runaway from an orphanage because Father Lavery is being transferred. The injured dog is a police dog identified by two officers who want to help. Lucy gets Tommy to open up.
Out exploring Lassie encounters a pair of nesting eagles. When the female injures her wing, Lassie alerts Ron and Keith who try to help. Lassie and her friends devise a way to help feed the chicks without disturbing the male.
Lassie befriends a high strung horse Midnight who belongs to Mr. Dobbs, a neighbor to the Holden Ranch. The stallion is being trained to race but a trip to the track ends in a mishap with Lassie on hand to help out.
Lassie and Lucy meet Joey, a runaway boy, when she is out riding. Bringing him to the Holden Ranch, he learns from the other boys about cattle and other farm activities. Joey overhears Keith on the phone and takes off again.
Because of the misunderstood phone call Joey runs away. After it's discovered Keith, Dale, and Ron start searching for on horseback in the rugged country. With the help of Lassie they discover Joey has fallen into a crevice.
Dale, Keith, and Lassie encounter Julio, who wants to build his dream house in an area with no water. Willie helps Julio build a well in a likely futile exercise. Dale and Keith want to include the older man as part of the ranch family.
While out in her own, Lassie's foot is severely damaged when caught in an illegal trap. She comes under the care of a reclusive Native American healer while Dale and Keith mount a search for their beloved animal friend.
Lassie alerts Willy to a dog floating down the stream and together they rescue the stray. At first the dog is fearful of country life but Lassie teaches the little animal which becomes important when a tree traps the collie.
Dale's new hobby is building and flying model airplanes so he is determined to retrieve one lost in a remote area. Dale leaves with Lassie and a new horse Midnight but the trip turns disastrous when a rattlesnake startles Dale near a cliff.
Dale is severly hurt after tumbling down a cliff with only an injured Lassie by his side. Lassie struggles to make her way to Midnight, hoping the horse will know to head to the ranch and alert Keith to the situation.
Lassie's stray dog friend gives birth in the Holden barn. Dale and Keith trail a coyote who takes a puppy into the mountains. They encounter two ranchers hunting coyotes as pests so Lassie teaches everyone a lesson.
Lassie, after accompanying Keith to the big city for Lucy's hearing operation, gets lost. Keith looks for her as Lassie wanders the city, taking in a kid's baseball game, the ocean but then enters an army firing range.
Lassie continues her journey home, getting a fish hook in her paw before being helped by Jim and his surfer friend. Accepting a ride north with his two new pals he nears the Holden Ranch. Lucy finds out if her hearing operation was a success.
Lucy, while hiking with Lassie, meets a traveling young Johnny who has a guitar and a dog Smokey. Her mother agrees to hire the troubled young man temporarily as he learns about life and what's important.