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
Tom Baker
Elisabeth Sladen
Nicholas Courtney
Richard Franklin
John Levene
John Dearth
Carl Forgione
Andrew Staines
Terence Lodge
Christopher Burgess
John Kane
Kevin Lindsay
George Cormack
Cyril Shaps
Chubby Oates
Pat Gorman
Terry Walsh
Michael Pinder
Stuart Fell
Geoffrey Morris
Ralph Arliss
Gareth Hunt
Jenny Laird
Joanna Monro
Walter Randall
Max Faulkner
Ysanne Churchman
Kismet Delgado
Maureen Morris