The Invasion, Part One

Having escaped from the Land of Fiction, the Doctor and his companions arrive in London in the near future: 1975. While looking for their old friend Professor Travers, they find a teenage girl named Isobel Watkins living in his house. Her uncle Professor Watkins is a close friend of Travers and has recently gone missing. The Doctor agrees to investigate his disappearance and begins his search at the London office of International Electromatics, the world's foremost supplier of all kinds of electronic equipment. Once there, the Doctor's suspicion is aroused by the company's managing director, Tobias Vaughan.