2. Dot and Bubble
Although "The Devil's Chord" warned fans that "There's always a twist at the end," many viewers were not expecting the twists and turns that "Dot and Bubble" offered. At first glance, the episode is a commentary on young people's over-reliance on technology, but that perspective soon faded into the background as it became clear just how vile POV-character Lindy really was.
The episode began with the premise of a world where people are literally encased in a digital bubble that tells them what to do, where to go, and how to function. When monsters started eating the people, the Doctor and Ruby had to try to save a girl who resisted being helped... at least by someone who was clearly "not one of us."
This is one of those episodes that sticks with you long after watching it. The structure of the story leads audiences to see Lindy as annoying but naive, only to eventually reveal the racism at the core of her society. Not only did she attack the Doctor for his skin color, but she and those in her community chose to go to their deaths before accepting help from a black man, showing just how destructive bigotry is to all people touched by it.