The TARDIS arrives in London in the near future, the Doctor and companions are enlisted by Isobel Watkins to find her father, a computer scientist working for International Electromatics. IE's director, Tobias Vaughn, arouses the Doctor's suspicions - confirmed by meeting Lethbridge-Stewart again (see "The Web of Fear"), recently promoted to Brigadier, who says that numerous other IE staff have gone missing. Lethbridge-Stewart now heads the British arm of UNIT, the United Nations Intelligence Taskforce, charged with investigating alien sightings and other such things.