10 MORE Doctor Who Episodes You Didn't Know Were Connected
2. The Moonbase & Nightmare In Silver
Written by the very talented and utterly mad Neil Gaiman, Nightmare in Silver whisks the Eleventh Doctor and Clara off to a theme park in spaaaaaaace.
There, they encounter the most horrifying force in the universe - overpriced snacks! Oh, and some Cybermen.
The metal nasties want to capture the Doctor and force him to become their leader. They half-achieve this, creating two personalities in one body - one is the Doctor, the other is the evil Mr. Clever.
The Doctor is initially able to overcome Mr. Clever by using gold, which Cybermen are weak to. This bit of lore was first established in Season 12's Revenge of the Cybermen, but it's not the only weird Achilles heel the Cybermen have.
Nightmare in Silver also mentions that Cybers can be stopped using cleaning fluid, which you might not know connects all the way back to the 1967 serial The Moonbase. Here, companion Polly concocts a "Polly Cocktail", a chemical mixture she uses to break down the Cybermen's plastic components.
She gets this idea after noting how a cleaning fluid like nail varnish remover is effective against plastic, a detail the Eleventh Doctor recalls all those years later.