While the City Administrator's schemes reach their climax, the Doctor and Ian venture into the tunnels under the city to discover the real cause of the Sensorite plague.

Starring:

Elisabeth Sladen, Frazer Hines, Jacqueline Hill, John Levene, John Scott Martin, Jon Pertwee, Katy Manning, Nicholas Courtney, Pat Gorman, Patrick Troughton, Peter Davison, Tom Baker, William Hartnell, William Russell

Genre:

Adventure, Drama, Sci-Fi