The Mitchell Vineyard, in the rolling hills of Northern California, is the very blood of Clovis Mitchell (James Stewart), a spare and dignified grandfather and guardian to Kelly (Stephanie Zimbalist) and her brother Chris (Michael Sharrett). The heart of the household, though, is Lassie, a handsome young collie, affectionate, obedient, sensitive, and very wise. A threat is in the air one night when Jamison (Pernell Roberts) and his associate Finch (Robert Lussier (actor)) appear at the winery and offer to buy the land from Clovis. They get a flat refusal from the old man, while Lassie growls in the background. Jamison promises to return, and does, to claim Lassie, one of a litter he says escaped during a fire. She has a tattoo mark in her right ear to prove it. Clovis has no alternative but to give up the dog, and tells his heart-broken grandchildren. Lassie has an alternative; taken by private plane to Jamison's home in Colorado Springs, Colorado, fitted with a handsome green collar with gold studs, Lassie makes her escape. Chased by helicopter and kennel men through the rocks and hills of Colorado, Lassie manages to elude them and out-stare a cougar before she joins up with new friends – Gus (Mickey Rooney), a down-at-heel wrestling manager and Apollo (Mike Mazurki), a kindly mountain of a man and Gus's so-called star.