Plot synopsis: Ruby Blackwell, typical young girl of Arizona, lives with her brother Tom, and their widowed mother in a cabin in the mountains. One day Tom takes Ruby on a lion hunt. They track a puma, or mountain lion. Tom shoots the beast, which, wounded, bounds into the canyon. Tom instructs Ruby to proceed to the ridge and await him there, while he follows the puma up the mountainside. Ruby discovers the cubs belonging to the puma which Tom has shot, and she immediately becomes so engrossed in playing with the huge kittens that she forgets the rendezvous her brother had appointed. Tom finally locates her. The cubs are taken home. They grow up around Ruby like friendly dogs. Pete Lopez, a bad Mexican, who admires Ruby very much, tries to steal one of them at night, after Ruby has refused to sell the animal to him, and the baby puma defends itself vigorously until Tom and Ruby rush to its rescue...