Trivia / Doctor Who S3 E2 "Mission to the Unknown"

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• Billing Displacement: Despite the Doctor not starring, William Hartnell is still credited. His contract stipulated that he would be credited every week, even if he did not appear in that episode. Purves and O'Brien did not have the same clause, although they were credited in the Radio Times listing.
• Missing Episode: One of only two standalone episodes from the original run (and the only one in the 25-minute format — the other was the 90-minute anniversary special "The Five Doctors"), and managed to become one of the missing due to tape wiping.
• Serendipity Writes the Plot: This episode came about because "Planet of Giants", which had kicked the second season off, was filmed and edited as 4 episodes, but then the BBC's Head of Serials requested it be edited down to three to quicken the pace. This created a one-episode hole at the end of the production season, and it was decided to make it a trailer for the forthcoming 12-part Dalek epic.
  • The unique status of "Mission to the Unknown" as a single-episode story featuring none of the main cast and only a handful of characters in total allowed for it to become the only missing episode to be completely recreated in live-action. For any other serial, this course of action would be prohibitively infeasible compared to animation or telesnap reconstructions.
• What Could Have Been: The reason the Varga plants are called such is because the planet was supposed to have the same name, and be a regular plant species.
• Working Title: Dalek Cutaway.
• You Look Familiar:
  • Jeremy Young (Gordon Lowery) had previously played Kal in "An Unearthly Child".
  • Barry Jackson (Jeff Garvey) had previously appeared as Ascaris in "The Romans".
  • Robert Cartland (Malpha) voiced the Rills in the preceding story "Galaxy 4".

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