On the planet Vortis, the Doctor and his companions aid the butterfly-like Menoptra in their battle against the parasitic Animus and its mind-controlled minions, the ant-like Zarbi.
The Doctor
Barbara Wright
Ian Chesterton
Vicki
Animus (voice)
Vrestin
Hrostar
Hrhoonda
Prapillus
Hlynia
Hilio
Hetra
Nemini
Zarbi
Zarbi
Zarbi
Zarbi
Zarbi
Zarbi
