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
CinemaSerf
Whilst the "Doctor" (Jon Pertwee) and the "Brigadier" (Nicholas Courtney) are doing some experimentation with a scientist with strong clairvoyant skills, "Capt. Yates" (Richard Franklin) manages to interest "Sarah Jane" (Elisabeth Sladen) in some curious goings on at a country retreat run by a kindl...