Two American astronauts on a hiking holiday in the Rocky Mountains. They see a UFO and watch it appear to land in a thickly wooded valley about two days' walk from them. They decide to try and find out as much about the landing as they can. After a couple of days trekking through the terrain, they eventually find the craft in the middle of a wooded valley and manage to gain access to it. They explore the craft and find that its crew are dead; they...