Based on Eric Knight's novel, a smart dog is sold by a poor family but keeps escaping to return to them.
Every day the collie Lassie accompanies Joe Carraclough (Roddy McDowall) home from school. Sam Carraclough (Donald Crisp) and his wife Helen (Elsa Lanchester) inform Joe that they have sold Lassie. The Duke of Rudling (Nigel Bruce) tells his granddaughter Priscilla (Elizabeth Taylor) that he bought Lassie, who is caged and refuses to eat. Lassie digs a hole and escapes to meet Joe at school. Joe takes her home, and Helen feeds Lassie. The Duke's kennel keeper Hynes (J. Pat O'Malley) takes Lassie back. This time Lassie climbs over the fence. Hynes comes to Sam, who goes looking for Joe and Lassie. Sam takes them back to the Duke and has Joe tell Lassie to stay. Priscilla tells Joe that she will take care of Lassie, and the Duke takes Lassie to Scotland.
Priscilla and the Duke object to the chain on Lassie, and the Duke orders Hynes to take Lassie for a walk with a leash. Lassie runs off, and Priscilla opens the gate. Lassie goes south. A shepherd shoots at Lassie, who fights off their dog. Lassie swims the river to England and is cared for by Dan (Ben Webster) and Dally Fadden (May Whitty). They realize that Lassie wants to go and open the door. Rowlie (Edmund Gwenn) gives Lassie food. The traveling Rowlie trains Lassie for his act. Two bums try to rob him; but they fight with Lassie, and the men run off. Rowlie says goodbye to Lassie. In a town the dog catchers chase Lassie, who jumps from a window and injures her leg. Sam tells Helen that he can't find any work. Lassie comes home limping. When the Duke arrives, Sam hides Lassie. The Duke hires Sam to work in his kennel and hears the dog. Priscilla pretends to agree with Sam and the Duke that this dog is not Lassie. Lassie goes to see Joe as school gets out. In the final scene Joe and Priscilla play with Lassie and her puppies.
This heart-warming story demonstrates the love and loyalty
an intelligent dog may show for humans.