10 Even MORE Doctor Who Episodes You Didn't Know Were Connected

Remember how Russell T Davies told the Radio Times that The Legend of Ruby Sunday would reveal that UNIT was harbouring "a long-buried secret" from the era of the Third Doctor?

Yeah, not quite.

Season 1's penultimate episode revealed that UNIT has had possession of primitive time travel technology since the 1970s. It's this technology that allows the Doctor and Ruby to revisit Christmas Eve 2004, to solve the non-mystery of Ruby's mother. The Doctor specifically refers to UNIT's tech as a time window, which you might've forgotten that we actually first saw all the way back in The Girl in the Fireplace.

Obviously, UNIT's fuzzy VHS holodeck isn't a patch on the impressive technology used by the Clockwork Droids, but it clearly works on a similar principle. The time windows in The Girl in the Fireplace and The Legend of Ruby Sunday can only take you to one specific location in one specific time period.

For the Tenth Doctor, the time windows allowed him to access various points in the life of Madame de Pompadour. For the Fifteenth Doctor, they allowed him and Ruby to watch a grainy old videotape scaled up to life-size.

Doesn't quite have the drama of riding a horse through a mirror, but it's an impressive bit of kit all the same.