11 February 1967
Patrick Barr (Hobson), Andre Maranne (Benoit), Michael Wolf (Nils), John Rolfe (Sam), Alan Rowe (Voice from Space Patrol) [1-3], Mark Heath (Ralph) , Alan Rowe (Dr Evans) [1, 3, 4], Barry Ashton, Derek Calder, Arnold Chazen [1-3], Leon Maybank [1-3], Victor Pemberton, Edward Phillips [1-3], Ron Pinnell [1-3], Robin Scott, Alan Wells, Mark Heath  (Scientists), Denis McCarthy (Voice of Controller Rinberg) , John Wills, Sonnie Willis, Peter Greene [2-4], Keith Goodman [3-4], Reg Whitehead [3-4] (Cybermen), Peter Hawkins (Cyberman Voice).
|Written by||Kit Pedler|
|Directed by||Morris Barry|
|Produced by||Innes Lloyd|
A mysterious virus is wrecking havoc among the crew of the Earth’s weather control station on the moon. While investigations into the strange disease are in progress, International Space Headquarters Earth puts the entire Moonbase into strict quarantine – The Doctor, Ben, Polly and Jamie included!
To take matters worse, the personnel of the Moonbase inexplicably vanish, and vital weather control equipment is sabotaged. Who is responsible? The Director of the base suspects the time-travellers. But The Doctor fears a ruthless enemy from his own past responsible that the evil Cybermen have returned