John is a cheerful and energetic young boy, who lives in a small coal-mining town in England. One day he finds a small dog lost in a flock of sheep. John takes her back home and names the puppy Lassie. Soon they become good friends, just like real siblings. Lassie is a very lovely and smart dog, so everyone in the town loves her very much.

But their happy life doesn't last long. Suddenly a coal-mine owner closes his company because there is no more coal left in the coal mine. John goes to meet the coal-mine owner to request a further investigation. The owner accepts John's request, but in exchange for that, he takes Lassie to Scotland.

Priscilla, the owner's granddaughter and also John's friend, cannot just stand by and let Lassie suffer in a cage. She opens the cage and sets Lassie free. Lassie sets out on a very long and hard journey from Scotland to her hometown.