It's 1938 and England is on the verge of war. Accordingly, the elderly but rich and playful Duke of Rudling (PETER O'TOOLE) is now watching over his granddaughter Cilla (HESTER ODGERS) in the English countryside while the girl's mother, Daisy (JEMMA REDGRAVE) stays in London and worries about her husband who's now in military training.
During a foxhunt, Cilla spots a beautiful collie that she likes, so the Duke offers to buy it from the working middle class Carraclough family. Since Lassie belongs to young Joe (JONATHAN MASON), his parents -- Sarah (SAMANTHA MORTON) and Sam (JOHN LYNCH) -- decline the offer. That is, until the mine where Sam works is shuttered, meaning the family needs the money.
Without Joe's knowledge, the transaction is made and the Duke's kennel handler, Eddie Hynes (STEVE PEMBERTON), takes the dog back to the regal estate. Yet, Lassie repeatedly frees herself and returns home, causing Hynes to accuse them of stealing the dog. With Lassie returned once again, the matter seems resolved when the Duke takes her and Cilla to his estate in Northern Scotland.
But the resourceful dog manages to escape yet again, embarking on an arduous, long and at times dangerous journey back home. While encountering a variety of characters along the way -- including traveling puppet entertainer Rowlie (PETER DINKLAGE) -- Lassie is determined to make her way back to Joe at any cost.