After years of prospecting, Jonathan finally strikes gold. He returns to town only to discover that his partner has since died and left his son, Tommy, fatherless. He decides to leave Lassie with Tommy to cheer him up.

In the meantime, Jonathan's new partner, Lin, isn't interested in sharing the gold, and tries to lure Jonathan to his death. Lassie immediately deduces what's happened and comes to the rescue.