Answering a distress call, the TARDIS lands on Earth on Christmas Day. The Doctor and Charley find the family of a girl named Zoe Elliot have been possessed by "Angels". The Angels believe Zoe is their missing daughter. Two thousand years ago there was a plague on their homeworld and they sent their daughter into space for safety. The journey to find her has led them to Earth. The Doctor explains that over the years the stars have moved. He uses the TARDIS to take the aliens to the proper planetary position, where they find their daughter.