After years of prospecting, Jonathan finally strikes gold. He returns to town only to discover that his partner has since died and left Tommy fatherless. He decides to leave Shep (played by Lassie) with Tommy to cheer him up. Meanwhile, Jonathan's new partner, Lin, isn't interested in sharing the gold, and lures Jonathan to his death. Lassie immediately deduces what's happened, so Lin poisons Lassie. Lassie barely pulls through and pursues Lin to a climactic confrontation where, due to an off-screen accident with some liquid nitrogen, Lin's gun jams.
Lassie gets thrown into some bushes, briefly knocking her out. She also gets shot, which causes her to whine a little. (We also see drops of blood in the snow) The worst part of the film happens before all of that, when Lassie is poisoned. Poor girl is shown whining and convulsing.(The dog actor, Pal, really sells it) The only saving grace, for viewers putting up with watching Lassie suffer, is that she is saved by an adorable terrier mix who alerts a Native American tribe to come to Lassie’s rescue.
Lassie has a few whining moments when missing her person, a few howling moments when grieving a loss, and actually becomes so depressed at one point, she stops eating long enough to need help from a medicine man.