A brother-sister duo, growing up at the end of a gravel road in the mountains of Montana, are worried sick. With radio silence from their dad, who took off a few years ago, and their mom now in trouble with the law due to her taking money from work to fix the family pickup truck, the siblings are left with limited options: hide or be separated in foster care. Full of anxiety, the kids fear what the foster care system will do with them, and they don't want to be taken away from their wonderful dog, Lightning. So, the sibling duo hatches a plan to use the family's backpacking equipment to hike to a high elevation where no one would think of looking for them. They hope to last the summer at the timberline, the zone where it's too cold most of the year, preventing tree growth. Catherine and Jim begin their trek up to high elevation, where they must cooperate to face the challenges posed by nature. They run into many obstacles, including an angry mama bear, creeks at flood stage, and a sudden snowstorm near the timberline that threatens their lives. However, they work together and can make it through the rough terrain of the mountains with some help from their beloved dog, Lightning.