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.
William Hartnell
Jacqueline Hill
William Russell
Maureen O'Brien
Catherine Fleming
Roslyn de Winter
Arne Gordon
Arthur Blake
Jolyon Booth
Jocelyn Birdsall
Martin Jarvis
Ian Thompson
Barbara Joss
Robert Jewell
Jack Pitt
Gerald Taylor
Hugh Lund
Kevin Manser
John Scott Martin