Lassie discovers a small, waiflike boy hiding in the barn, but the child won't talk. The Millers soon find out he's Timmy, an orphan living in Olive Branch with his elderly relatives, Uncle Jed and Aunt Abby Clausen. (Some type of accident killed Timmy's parents.)
Timmy is so excited about his new suit that Ellen allows him to wear it until Jeff gets home, but when he tears it, afraid they will send him back to his aunt and uncle, Timmy lies and lays the blame on Lassie. To make him confess, Ellen makes him decide Lassie's punishment.
Jeff is thrilled to accept a summer job at Doc Weaver's office, but when he neglects his duty for a few minutes, a potentially rabid dog is let loose
When Timmy and Lassie find a sick burro, abandoned by neglectful but well-meaning owners, everyone thinks Timmy's exaggerating until Ellen finds the creature. Timmy's faith and the family's nursing save the burro, but then her owners come return.
With Jeff at the dentist, Timmy and Gramps go out to pick huckleberries for pies for the church supper. Timmy thinks Gramps is ill when he naps after berrying, but it's Timmy who must be rescued after eating nightshade berries.
Timmy and Jeff nurse an injured raccoon against protests from Gramps--and ""Sam"" repays them by wreaking havoc in kitchen, barn, and chicken coop. Released to the wild, he returns to begin stealing things from the house.
Jeff tries every way he can to avoid meeting Debbie, the daughter of Ellen's visiting college roommate Lucy Hopkins--until he sees her dance and is smitten. But when Porky lampoons her dancing, Debbie tells both boys off.
Jeff and Timmy saw a huge elephant. Ellen & Gramps doesn't want it as an 2nd Pet for Lassie. They decided to keep it until the animal control person comes by and wanted to get rid of the elephant.
Timmy believes he and Lassie are unloved and unwanted by the Martins, and sends Lassie to the Millers in Capitol City. Ellen Miller, knowing that Timmy is mistaken, returns to the farm to reunite Timmy with his loving adoptive parents.
Timmy borrows a bike to learn to ride, but when the bike is stolen, he must replace the stolen one with his new bicycle. The situation is resolved when Lassie plays detective to hunt down the bike thief.
Paul, Timmy, and Lassie are stranded on a deserted road when Paul realizes Timmy is becoming seriously ill. Lassie must risk her life to bring help to the sick child.
When Timmy and Scott launch a bait-worm selling business, their only potential customer refuses to buy anything. He changes his mind, however, when Lassie saves him from drowning.
Timmy believes one of Uncle Petrie's tall tales and is hurt to discover he has been lied to. A gift of a friendship ring, crafted by Uncle Petrie himself, mends their relationship.
Timmy comes running home with a story about a rabbit-sized pony--but no one believes him.
To replace Uncle Petrie broken guitar Timmy enters a borrowed parrot in a contest to win the prize of a new guitar.
Timmy refuses to attend the Grange Square Dance out of fear that he will have to dance with a girl. After Uncle Petrie reassures him this will not happen, he relents. To everyone's surprise, a fire disrupts the children's dance and Lassie must save the day.
A drought is hitting the area pretty hard, and Timmy desperately attempts to keep his own small garden from perishing.
When Timmy insists on going to a blasting site despite Lassie's protests, she is struck on the head by a dynamite-propelled rock and appears to not know who she is. Then she wanders away from the farm.
Members of the community band together to hunt down deer driven to eat their crops, but Timmy and Scott fight to do something that doesn't involve killing them.
Timmy is stricken with severe stomach cramps and keeps calling out for Lassie.
A crate holding a penguin enroute to the Capitol City zoo falls off its truck, and Timmy and Scott adopt the creature
Timmy tends an injured sparrow.
When Lassie finds an injured seeing-eye dog, the family searches in vain for the dog's owner. The situation appears hopeless until Lassie leads them to the dog's missing collar, and a telephone call to Capitol City Hospital reunites dog and owner.
Timmy becomes overzealous in his efforts to spot fire hazards to win a contest.
Ruth tries to replace Lassie's disreputable old blanket with a new one, but Lassie will have none of it.
Timmy's new rabbits take precedence over Lassie.
Scott's city cousins make fun of Timmy and Scott's interest in the Cub Scouts
Timmy's ""patient,"" an injured crow he names ""Peck,"" recovers to become a farm pest.
On the sly, Lassie tends some orphaned puppies.
Timmy becomes annoyed with a house guest of Ruth when all she can talk about is all the finer things Ruth is missing by living on a farm.
Inspired by Uncle Petrie's tale of a boy who talks to the animals, Timmy sets out to befriend animals himself. But he helps some people along the way and it is their friendship and kindness that save Lassie from a precarious situation.