Doctor Who: The Silent Stars Go By

The winter festival is approaching for the hardy colony of Morphans, but no one is in the mood to celebrate. They're trying to build a new life on a cold new world, but each year gets harder and harder. It's almost as if some dark force is working against them. Then three mysterious travelers arrive out of the midwinter night, one of them claiming to be a doctor. Are they bringing the gift of salvation or doom? And what else might be lurking out there, about to wake up?