England, the near future. As the Doctor receives a parcel from South America, Mike Yates asks Sarah to visit the meditation centre where he's been recuperating. But what is the true significance of the blue crystal of Metebelis Three? And is this adventure one too many for the Doctor?
Elenco: William Hartnell , Patrick Troughton , Jon Pertwee , Tom Baker , Peter Davison , Colin Baker , Sylvester McCoy .