The blue crystal that the Doctor took from Metebelis III in a previous adventure is desperately sought by the Eight Legs, a race of mutated spiders, as the final element in their plan for universal domination. With help from an old mentor, the Doctor realises the only way to foil the plot is to make the ultimate sacrifice. The Doctor must risk death to return to the cave of the Great One and save the universe.
Jon Pertwee
as The Doctor
Tom Baker
as The Doctor
Elisabeth Sladen
as Sarah Jane Smith
Nicholas Courtney
as Brigadier Lethbridge-Stewart
Richard Franklin
as Mike Yates
John Levene
as Sergeant Benton
John Dearth
as Lupton
Carl Forgione
as Land
Andrew Staines
as Keaver
Terence Lodge
as Moss
Christopher Burgess
as Barnes
John Kane
as Tommy
