5 March 1966
Eric Elliott (Commander), Inigo Jackson (Zentos), Roy Spencer (Manyak), Kate Newman (Mellium), Edmund Coulter (1st Monoid), Frank George (2nd Monoid), Michael Sheard (Rhos), Ian Frost (Baccu), Stephanie Heesom (1st Guardian), Paul Greenhalgh (2nd Guardian), Terence Woodfield (Maharis), Ralph Carrigan (Monoid Two), Terence Bayler (Yendom), Edmund Coulter (Monoid One), Brian Wright (Dassuk), Eileen Helsby (Venussa), Frank George (Monoid Three), Roy Skelton (Monoid Voice), John Halstead (Monoid Voice), Richard Beale (Refusian Voice), John Caeser (Monoid Four)
|Written by||Paul Erickson/Lesley Scott|
|Directed by||Michael Imison|
|Produced by||John Wiles|
Materialising in what appears to be a jungle on Earth, The Doctor, Steven and Dodo soon realise that things are not what they seem: the sky is made of steel, and the jungle merely a colossal life chamber in a craft that has embarked on the most important expedition in the history of mankind.
It is ten million years in the future, and the Earth is soon to be engulfed by the Sun in a catastrophic explosion. A gigantic space ark has been launched, taking the last humans to a new life on the distant planet of Refusis, serving the Guardians of Earth are the Monoids, mute reptilian aliens.
But the Ark’s mission of deliverance is threatened by the arrival of the time travellers, Dodo inadvertently passes her cold to the Guardians – to them, it is a long-forgotten virus against which they have no defence. It is not long before people start to die and the TARDIS crew are on trial for their own lives.