The TARDIS arrives on the planet Vortis. There the Doctor and his companions discover and become involved in the plans of butterfly-like creatures (Menoptra) to reclaim their planet from a spidery parasite that is steadily enveloping it in a web-like structure. They join up with a party of Menoptra and their allies (the underground-dwelling Optera) and manage to destroy the parasite.
Elenco:
William Hartnell
,
Patrick Troughton
,
Jon Pertwee
,
Tom Baker
,
Peter Davison
,
Colin Baker
,
Sylvester McCoy
.