While playing and chasing a rabbit in San Carlos Canyon, Lassie and her old friend Spike are caught in a flash flood and trapped in the river as the waters rise. Rangers Corey and Barney work in tandem to rescue their beloved canines.
While in the desert visiting an old friend, Lassie and Corey meet an injured seagull. When he escapes his cage, Lassie protects him from several predators before he can accompany Lassie and Corey back to the ocean when they return home.
A serious reduction in trout has caused Andy McGrew's business to fall into disrepair. Lassie, Corey and a man from the fish and game department discover the cause of the problem with the trout and help Andy save his business.
During heavy rains and flooding, a group of logs break free and float down river. Lassie and Ranger Corey battle the rapids to string a chain line across the river to constrain the logs and save a bridge construction project.
In the Bristlecone National Forest where the bristlecone trees are ancient, the earth is fragile, and no off-road vehicles are allowed, two cyclists threaten the safety of the environment as well as the safety of Lassie's new friends.
After an outbreak of rabies is confirmed in one of their campsites, Lassie and Ranger Corey Stuart search for a boy who may have been bitten by a rabid squirrel and must be stopped for medical attention before he can leave the area,
When land is being cleared and burned to create new grazing land for cattle, Lassie plays protector to a family of rabbits caught in the upheaval. She helps them relocate and protects them from predators during their move.
Corey and Lassie visit a ranger whose wife is having trouble adjusting to her new life in the forest. When a ranger at Red Oak Station is attacked by a wounded bear, the wife and Lassie must assist the ranger and deal with the bear.
After a car accident injures a pregnant collie and her master, the collie tries to seek help for them. While Corey offers medical assistance to the young man, Lassie finds shelter for Lady and stays with her while she delivers her pups.
While visiting a town whose lake is drying up, Lassie and Corey try to determine what's causing the water to recede. When Lassie finds a new source of water, the townspeople must find a way to release it into the lake.
During a nature walk Lassie brings a bag of treats to feed her animal friends. She .springs a hunter's traps and befriends a skunk, who follows her. When a hungry wolf shows up to fight Lassie, the skunk steps in to help.
Ranger Henry's Aunt Sam arrives with Rufus, a homesick hound. They're moving into the area and are searching for a house. Lassie discovers and reveals the reason why Rufus is homesick and what he wants in a house.
Corey and another ranger battle a spruce bud worm infestation by spraying but meet resistance from a horse ranch owner. Lassie makes friends with a colt and reveals the true cause of death of one of the horses.
Young Mike runs away from a detention farm stealing items from a nearby house. He also saves a colt and befriends Lassie. Corey tracks Mike with the collie's help, then tries to convince him that both he and Lassie are friends wanting to help.
When the rangers are too busy to play with her, Lassie goes for a walk in the woods and finds two baby raccoons whose mother was forced downstream by a hungry coyote. Lassie babysits until the mother raccoon returns.
Lassie and Corey assist a scientist who has invented a nuclear probe to measure snow packs. When the scientist has a cardiac event and Corey suffers from snow blindness, Lassie must lead the two men to safety.
Ranger Corey gets a call from Steve regarding a lost girl Kathy and takes Lassie along to search. They locate her at the bottom of a cliff but her recovery hinges on finding her missing doll. Lassie heads out to find it.
Lassie visits her friend Boone Sawyer who does not want power lines coming into the forest. When a surveyor gets stranded, Boone has a chance to argue his point of preserving the beauty of the wilderness from the ugliness of technology.
Lassie and Corey work at a summer camp for handicapped boys. Most of the boys were born deaf, but one young man is severely traumatized from an automobile accident. Lassie and a squirrel help him overcome his problem after an earthquake.
Lassie finds a small dog near a rock slide and tries to lead his new friend to safety. But the collie doesn't know that a person is trapped beneath and the man's pet refuses to leave until he's rescued.
To get timber cut and moved before an impending snow storm, a lumberjack makes a risky climb to "top" a tree. Corey must help the lumberjack while Lassie clears out the wildlife on the ground to protect them when the tree falls..