50 years ago: The Faceless Ones [http://tardis.wikia.com/wiki/The_Faceless_Ones_(TV_story)] was the eighth story of season 4. Companions Ben Jackson and Polly, played by Michael Craze and Anneke Wills respectively, left the series at the end of this story. Guest stars included Pauline Collins as Samantha Briggs [http://tardis.wikia.com/wiki/Samantha_Briggs] and Benedict Cumberbatch’s mother, Wanda Ventham as Jean Rock [http://tardis.wikia.com/wiki/Jean_Rock] Additionally, the original rendition of Delia Derbyshire’s opening theme for the series was replaced with a new arrangement [Who Productions YouTube Channel].
The TARDIS arrives on Earth in July, 1966, on a runway at Gatwick Airport. Polly witnesses a murder in a nearby hangar and is then kidnapped by the perpetrator, Spencer of Chameleon Tours. Ben also vanishes. The Second Doctor and Jamie are left to convince the sceptical airport Commandant there has been foul play.
A great many other young people have also vanished, all of them on Chameleon Tours holidays. With the help of Samantha Briggs, the sister of one of the missing youths, the Doctor and Jamie uncover a plot by the alien Chameleons to kidnap human youngsters to take their identities, for the Chameleons have lost their own identities in an accident on their home planet.
The Doctor offers to help the Chameleons find another solution to their problem, and the kidnapped humans are released.
45 years ago: The Mutants [http://tardis.wikia.com/wiki/The_Mutants_(TV_story)] was the fourth story of season 9. Its narrative inspiration was very similar to that of Colony in Space. Whereas Malcolm Hulke had based the earlier story on the struggle of Native Americans against European settlers, here Bob Baker and Dave Martin explicitly based their story on South Africa and the segregationist policy of Apartheid, which had also inspired Ian Stuart Black’s The Savages. By the recording, however, director Christopher Barry had de-emphasised the political allegory in favour of the story’s science fictional elements. One such element came from an unused 1966 Barry Letts story submission, itself entitled The Mutant. Forming the main plot of the later episodes, this Letts-inspired subplot focused on a species maturing in radically different physiologic phases, like a butterfly. Guest stars included Geoffrey Palmer as Administrator [http://tardis.wikia.com/wiki/Administrator_of_Solos] and John Hollis as Sondergaard [http://tardis.wikia.com/wiki/Sondergaard], lated Lobot in The Empire Strikes Back.
The Time Lords send the Doctor and Jo on a mission to deliver a sealed message pod to an unknown party aboard a Skybase orbiting the planet Solos in the 30th century. They are caught quickly in a power struggle between the cruel Marshal of Solos and the young Solonian Ky over the future of Solos — a future that hinges on the contents of the message.