Lassie, on her own now (no explanation is given), meets a young man traveling the countryside and his male collie, Duke. They later find haven, and the young man a job, at a ranch where the owner's young son has not spoken for years.
While Duke and his master move on, Lassie remains at the ranch, but her new puppies are endangered by the owner, who thinks the pups were sired by a killer dog.
Lassie and her three puppies escape from the ranch and head for the desert, where Kerry discovers them and helps them survive.
Mute Kerry continues to help Lassie and her puppies elude his father and the sheriff, who's determined to kill the pups, and by the time the rancher learns Duke was the father of the puppies, it's almost too late.After everything is revealed, Kerry's father let's him adopt one of Lassie's puppies.
In this all-animal episode, Lassie teaches her two remaining puppies to survive in the wild, not an easy task in an area full of snakes and predators.
Lassie and her puppies meet a boy who is grief-stricken by the recent death of his dog.So Lassie leaves one of her two remaining puppies with the little boy.
While wandering the forest, Lassie and her remaining puppy meet a little girl who can ""talk to animals.""
Lassie befriends an elderly man whose claim that the flock of birds he feeds love him is scoffed by his cynical checkers opponent. But the faithful birds will surprise them.
After a forest fire, Lassie helps the wild animals displaced by the flames find new homes.
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.
Lassie and a workaholic trucker rescue a young man traveling across America trying to live ""a year of Sundays"" after getting out of the Army. The trucker scoffs at Mark's idea--until the brakes fail on a steep downhill run.
Lassie takes refuge during a rainstorm in the garage of a good-hearted, lonely widow whose children have gone to college, but the woman is reluctant to let the muddy collie into her tidy house. Then the loose earth behind her house, weakened by water, begins to slide.
Lassie and an injured mother linnet, who was stunned by a car while foraging for food on a road, bring together a lonely man and woman; in caring for the injured creature, they also learn to open themselves to each other.
The ring-tailed cat Lassie saves from a bobcat becomes the hunter after he goes after a grouse's nest along with a grey fox; next, a horned owl's nest is threatened by an opossum. After Lassie deals with the possum, she enlists the grey fox's help to rescue a burrowing owl from a ferret. Then the bobcat returns to stalk the horned owl's nest
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.
A boy restless with his rural life and chafing under the ""no trespassing"" signs of their territorial neighbor wishes to strike out to ""follow his star""--stealing the neighbor's mare to do so.
Teenage Patty, reluctantly having left the city for a summer in the country with her aunt, has an inauspicious beginning: she's poisoned by arsenic in the well. Her aunt finds the source of the problem in an old mine, but is then trapped when the floor collapses, so Lassie must find Patty, who's just about to leave.
Lassie and her new pal, a mutt named Skipper, are getting along just fine with Reed and Johnny, a couple of guys they befriended on the beach, until John discovers Reed is ""the law,"" a harbormaster, and walks out. But he finds he needs ""the law"" later on when he ""borrows"" a for-sale cabin cruiser and takes Lassie and Skipper along for the ride.
Lassie returns to visit the farm where she left one of her puppies--and once upon her way again, falls down a hidden well.
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.
People who have been helped by Lassie (including the couple from ""Gentle Dawn,"" who are now married) help rescue her from the well.