McKenna Barney is trying to hide her worsening eyesight and has been isolating herself for the last year. But at the request of her little sister, she signs up for a commemorative mail run race in the Canadian wilderness—a race she doesn’t know if she can even see to run.

Winning would mean getting her disease—and her sister’s—national media coverage, but it would also pit McKenna and her team of eight sled dogs against racers from across the globe for three days of shifting lake ice, sudden owl attacks, snow squalls, and bitterly cold nights. Can courage alone see her through?