Doctor Who episode 217: The Mind Robber – Episode 3 (28/9/1968)
The risk of a story like this is that, like a Terry Nation script, it can be prolonged almost indefinitely by bunging in another confrontation with a creature from literature or legend. So it’s to the story’s credit that not only do the episodes run shorter than usual – this clocks in at 19 minutes – but that there’s some thematic coherence and structure that prevents this from feeling like a piece of derivative whimsy.