England, the near future. Wenley Moor research station is experiencing strange power losses, and off-duty staff have been killed while potholing in the local caves. What ancient force has the station reactor re-energised? And is Man's civilisation really the only one in Earth's history?
Elenco: William Hartnell , Patrick Troughton , Jon Pertwee , Tom Baker , Peter Davison , Colin Baker , Sylvester McCoy .