It is rare that wolves will attack livestock, so when local Rancher angrily report that their cows are being killed by a vicious wolf, Sarah decides to head into the back-country to figure out what's really going on. With Zoe, Harvey and Lassie along, Sarah hikes into the high country to observe the wolves and see if the Ranchers' accusations could be true. When she discovers the real culprit, Sarah and the kids find themselves in a dangerous situation and only Lassie can save the day.