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.

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Main Cast: William Hartnell, Jacqueline Hill, William Russell, Maureen O'Brien, Catherine Fleming, Roslyn de Winter, Arne Gordon, Arthur Blake, Jolyon Booth, Jocelyn Birdsall

Director: Richard Martin

Writer: Bill Strutton

Editor: Gitta Zadek

Cinematographer:

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