Miss Ridgeway is an artist who lives in an isolated area who is also a diabetic. When a fire destroys her supply of insulin it is up to Lassie to get her to safety.
After two tourists discover a fawn and feed and handle it, Corey and a local ranger fear the doe will no longer accept it and the fawn will have to live in captivity. Lassie is able to find the doe and convince her to accept it again.
While Corey and two other rangers blast snow for avalanche control, Lassie deals with a rabbit and a fox. First she saves the rabbit from the fox; next she feeds the fox a sandwich; finally she saves them both from the snowfall resulting from blasting.
While in Florida visiting a friend in astronaut training, Corey and Lassie meet Atlas, a dog who lost his handler, has gone rogue, and is hurt. When Atlas gets trapped in muck in the swamp, Lassie brings help to rescue him.
Still at Cape Kennedy Lassie and Corey meet a boy who has lost his dog. Lassie brings the boy to meet Atlas and later takes Atlas to the boy's house. Atlas accepts water and goes into the doghouse to rest. The building of trust has begun.
At Cape Kennedy the testing of parachutes for the lunar module injures an American bald eagle. The race begins to see which bird will launch first: the lunar capsule or the bald eagle.
After obtaining a permit for his performing animals to put on a camp show, Tom Whitney's brakes fail and his truck crashes. His dog goes for help and Lassie must gather up the four escaped animals while Corey gets Tom to the hospital.
At Pine Lake to begin a Wilderness Project by acquiring land through a series of land exchanges, Corey and Lassie meet the Hanford brothers. When Lassie falls down a mine shaft, the brothers and a local girl named Lucy rescue her.
When Corey leaves Lassie with the Hanford brothers, she alerts them to an accident their friend Lucy has on the lake when her boat has mechanical problems and she must swim to safety. The experience leaves Lucy hospitalized with pneumonia.
Since the Hanford brothers rescued Lucy and got her to the hospital, her father agrees to help them with their house after they have a setback in construction because they ignored warnings from Corey, Lassie, and a crow named JR.
When Stuart's truck is blocked by a landslide, Lassie must deliver an injection to counteract mineral poisoning in an important banded Canadian Goose in time for it to be effective to a female employee on assignment at the station.
Lassie races for help after an earthquake traps Corey under a tree in the path of a rock slide. Unfortunately the motorist who finds Lassie confines and drugs her then sells her to a vet conducting animal experiments.
While accompanying smoke jumpers, Corey and his partner Lane are trapped in the path of a fire. Both rangers are badly burned and rushed to the hospital. Lassie tracks them but encounters ranger Bob Erickson, who takes over caring for her.
The Forest Service must decide Lassie's fate after they realize Corey's recovery will take months. Lassie escapes from Ranger Bob's trailer to go to the hospital just as Corey is transferred to another one. Lassie has a decision to make.
While Scot is taking a tour with a bush pilot of Scot's new assignment in the National Forest of Alaska, a man in distress is spotted and on landing he finds the man has been attacked by a companion delirious following a bear attack.
Scott and Lassie are introduced to Johnny's adopted brother Neeka. The rangers survey an island where they rescue a female eagle that has fallen into the lake. Meanwhile Lassie protects the baby eaglet from a lynx.
While Dean and Scott continue to survey the water areas, Neeka and Lassie go fishing. When Lassie breaks her leg in a trap. Neeka must take charge of the situation. Meanwhile a wolf stalks the injured Lassie.
While repairing a gas leak on their boat Dean is knocked unconscious, so Lassie swims for help. She finds Neeka and Scott who are finishing up a series of glacier studies. Then they must wait for the Coast Guard to complete the rescue.
The livestock of a ranch on which Scott is taking samples to see if more grazing can be allowed is menaced by a jaguar from which Lassie must defend the ranch hound during an attack.
After Scott and Paul chase off a puma that has chased a jaguar from the injured hound Jason, Lassie leads Scott joined by Billy to track down and kill the jaguar.
Scott and Lassie visit Bob Erickson, who's affliated with a California university oceanography division. Lassie helps free a pelican tangled in a net then the bird returns the favor when Scott and Diane are trapped taking underwater photos.
When Bob and Al give the horses salt water therapy, Lassie protects a lost kitten from the perils of hawks and sea water while preventing a horse broken free after a bee sting from straying afar.
Two brothers have raised a calf as their 4-H Project. Russ had made a pet of Butch and wants to keep him while Ken wants to sell him for beef to pay their college tuition. When Butch wanders away, Lassie assists with the situation.