Students Sonja Rendell and Marni Sheppeard are on a 3-day hike in Arthur's Pass National Park, staying in picturesque huts and planning to visit thermal mud pools, before returning home for a family Christmas. But when their path is blocked by ice, the girls take a detour. What started as a steep slope quickly becomes a sheer cliff - with Sonja clinging to the rock with just her finger tips. Returning to the trail is no longer an option as the girls fight to survive on a tiny rock ledge in torrential rain and wind. Will Sonja and Marni be able to climb their way to safety?