While Corey examines an area to assess damage after an earthquake, Lassie becomes involved with first a duck and then a prairie dog town who are rebuilding after the quake. Then an aftershock brings even more trouble.

Stuart helps a crew extinguish an oil well fire during which process Pat's terrier is badly injured and requires a transfusion from Lassie.

Corey and Bart enlist a sail plane pilot to learn about wind sheers, while Lassie helps a pregnant cougar who has been mistakenly shot by a farmer for raiding his chickens. The real culprit is a feral dog.

While Corey learns more about wind sheers, Lassie protects the injured cougar and her newborn cubs and feeds them by stealing meat from the ranch and bringing it to them.

A wild animal is by night stealing poultry and frightening the horse Starfire. The foreman thinks it is a cougar who has done this and wants to shoot it, but Lassie understands that the cougar is innocent. When Lassie finds out that the cougar has cubs but is too wounded to feed them, Lassie has to find meat for them and protect all of them from being shot.

Unless something changes, Corey is convinced Fawn Lake will be ruined. With Lassie's assistance, Corey tries to convince a businessman named Kirby that his boat rental service is the primary polluter.

Lassie protects a ring-tail and ground birds along with their chicks and eggs from predation by a bobcat, a coyote, a weasel and an opossum.

Pristine Fawn Lake is becoming polluted and Lassie's friend Corey meets a photographer he thinks can help change things.

Corey, Lassie, and their pilot are trapped when their small plane makes a forced landing on a glacier. Not only is the plane damaged, but also Jack has broken ribs and a storm is coming.

Corey and Jack fix the plane before the storm breaks, but every pound is precious. When Jack insists that the aircraft will not be able to take off with Lassie's added weight, Corey rigs a device so she can be picked up after the plane is in the air.

Lassie trails an adventuresome cat called Dandelion around a logging camp. It leads to several dangerous situations for the animal friends.

In his capacity as advisor for a new balloon logging project, Corey inspects a tugboat operation. Corey and Lassie journey on two different boats. When the pilot of Lassie's boat has a stroke, Lassie must find Corey to get help for him..

At the Wind River tree nursery deer are eating the seedling trees. Rather than see the deer shot, Lassie moves the family of deer across a bridge into a wildlife preserve. When the fawn strays into the river, Lassie helps it to safety.

Corey's reforestation project runs up against Bob Stokes who sees himself as the protector of the trees in Oregon. Corey, Merle, and Lassie are shown how hot air balloons are used to transport timber.

Delivering trees on Christmas Eve, Lassie and Corey find and free a dove tangled up in brush. The dove repays the favor by leading Lassie to a little girl's lost puppy so that Lassie can return it to the worried child.

Out delivering treats to her forest friends, Lassie finds a lost black lamb. She reunites that lamb with its mother only to find a lost white lamb. After finding that lamb's mother, Lassie finds a lost black and white lamb. She howls her frustration before setting out to find that lamb's mother.

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.

Lassie rescues a coati-mundi's wayward kit and a lost lamb as well while Corey and his compatriots battle the forest fire threatening their home.

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.

Boy Scout Hank takes a tumble off the trail and lands on a disintegrating ledge. Lassie discovers him and must find help quickly before it's too late.

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.