After Timmy, without thoroughly searching for the terrier's owner, gives a terrier he has found to a neighbor boy despondent that his orphan status has displaced him from France, a pet shop proprietor comes looking for the dog.
Lassie receives a wound saving Cully from the shot of a careless deer hunter and the family must persuade a neurosurgeon temporarily in Capitol City to operate on a dog to prevents Lassie's paralysis from the bullet's movement.
Timmy helps a boy whose carelessness has resulted in paralysis to his Labrador retriever build a cart to allow the dog some freedom of movement but the boy's Labrador breeder father thinks the dog's destruction is best.
So that Mr. Washburne's fish will not be ineligible in a contest because Lassie found it, Timmy has to hide that Lassie can find large fish despite that he will be rebuked for creating a news story frenzy by telling Lassie's ability.
At the county fair Jake Hodges who has a hot air balloon befriends Timmy and Lassie, but when the hot air balloon start to drift away, Timmy becomes trapped in the balloon while trying to stop it with Lassie jumping in to save Timmy and together they drift away.
The hot air balloon with Timmy and Lassie is caught in tree branches in the Canadian wilderness and Timmy must now find a way down and to find water once they are on land.
Landing in the woods from the hot air balloon journey, Timmy must resort to his scout survival skills to find food and shelter, but is sidetrack when Lassie is attacked by a wild boar.
When Lassie developed a fever after being attack by a boar Timmy find a river to cool Lassie and is convinced that following the river in a raft he built will lead him to people for help.
When the raft Timmy and Lassie capsizes they become separated, Lassie is cared for by a deaf-mute Indian, while Timmy is reunited with his parents Lassie must find his way back to Timmy.
Learning that traditional bluebird nesting sites are declining, Timmy builds birdhouses for the area to preserve the species but the preservation project is imperiled when the local farmers use dynamite to combat a starling invasion.
Neighbors grow angry with Cully who has falsely warned them of an impending frost when he misinterprets strange animal behavior but Lassie helps Cully reinterpret the behavior as a coming twister so he must use Paul to spread the word.
A turkey farmer whose poults are being raided by an owl accuses of rustling a transient who has scavenged a chick that Lassie has caused the owl to drop.
Cully borrows from the Martins to enter a burro race at the county fair hoping to win funds to buy some land before neighbor Krebbs can but draws a puny, stubborn female only Lassie can handle. Meanwhile Krebbs locks Lassie in his barn.
A bag of pine cones that Timmy is assigned from his class by a forest ranger to collect for seeds to use in a flood break planting is washed away by runoff when Timmy leaves the bag in the woods because it is too heavy.
After Cully suffers a heart attack he worries about his farm, but Timmy offer to help on the farm with Lassie. Timmy encounters a gopher problem and uses a weasel to counterattack the problem but the weasel becomes a problem too.
An army dog that accidentally injures its trainer flees and follows Lassie home where its training is mistaken by a fearful Timmy and Ruth for unreasoned aggression.
Participants in a pigeon race Timmy has organized are very angry when the pigeons do not return because everyone is unaware that radar operating in the area has interfered with the pigeons' navigation.
On her way home from shopping in Capital City, Ruth skids on the dangerous muddy cliff road and is left teetering in their pickup truck on the edge of a cliff. Lassie to the rescue.
When Timmy friend Ricky returns to France he gives his dog to Timmy, Timmy however gives the dog to Cully after the death of Cully's dog. But the new dog causes Cully problems and Timmy begins to regret his decision.
As a result of Washburne showing a fire prevention film at the school, Timmy removes fire hazards from Charlie James' barn creating an unintended disturbance which causes James to petition the city to remove Washburne as chief .
When Timmy and Cully visit a abandoned cabin of a deceased man who supposedly had a hidden treasure hidden away they come across an eagle inside clutching a pouch which Timmy believes to be the hidden treasure.
Cully leg is trapped by a boulder after being caught in a landslide when he and Timmy were trying to get to the eagle's nest to get a pouch which they believe to be missing hidden treasure.
While looking for butterflies for a nature school project in the Martin peach orchard Timmy and Lassie discover the orchard has been infested by the destructive gypsy moth.
When Timmy enters a Camera Club contest Timmy attach a camera to a kite to get a aerial photo, but kite and camera get caught on a high tension power wire over a neighbor stable which catches fire from the sparks.
During a time when Timmy has organized a wild animal feeding program in a severe winter for which the local farmers blame a surge in wolves, a quaint toy repairman traveling with a donkey wagon lodges with the Martins at Christmas.
It is a bustling Christmas for Calverton as Timmy sings a solo at church and the Martins host a party while Lassie rescues the cubs of a wolf Krebbs has killed and Nicholson disappears with the cubs as mysteriously as he arrived.
Timmy is begrudgingly allowed by the Martins to raise an orphan colt that is born blind and with Lassie's help overcomes challenges he experiences in the process.