Doctor Who/Recap/S18/E03 Full Circle

"Login: A little patience goes a long way. The Doctor: Yes. Too much patience goes absolutely nowhere."

The TARDIS is on its way to Gallifrey to return Romana home, a task the Doctor has been putting off (and Romana has been letting him) for over a season, when it falls into a Negative Space Wedgie. The result is apparently only a momentary disturbance, but when they arrive at their destination, it isn't Gallifrey. They're in the right place, and the right time, but—they eventually discover—the wrong universe. (For ease of discussion, they subsequently dub the two universes "Normal Space" and "Exo-Space", or "N-Space" and "E-Space" for short.)

Meanwhile, the inhabitants of the planet that isn't Gallifrey have problems of their own. Years ago, a starliner from the planet Terradon made a crash landing on the planet, where they were attacked by the local lifeforms. The survivors of the attack set about trying to repair the starliner and return to Terradon, a task at which their descendents are still working. And now the season of Mistfall is approaching, when all take shelter within the hull of the starliner to avoid the mysterious dangers lurking in the fog. But there are dangerous mysteries inside the starliner as well.

At the end of the story, Adric, one of the people from the starliner, stows away in the TARDIS.

Tropes

 * Death by Origin Story
 * Fog of Doom
 * Forgotten Fallen Friend: Adric only mentions his brother's death once after this story and seems to suffer no emotional repercussions from it, much to the chagrin of Matthew Waterhouse (see Reality Subtext below).
 * Friend to All Children
 * Healing Factor: It's a bit of a plot point in this story that all of Adric's people can heal faster than human normal. You'd think this would be handy for a companion, but it turns up once in Adric's stories and then never again.
 * In Harm's Way: Romana really doesn't want to stay on Gallifrey again.
 * Negative Space Wedgie
 * People in Rubber Suits: The Marshmen
 * Plug N Play Technology
 * Promoted Fanboy: Writer Andrew Smith and actor Matthew Waterhouse were both card-carrying Doctor Who fans before their professional associations with the show. In fact, Andrew Smith (who was nineteen when this story was written) is one of exactly two writers to have written for the show without having had any prior professional writing experience. (The other was Marc Platt, who wrote "Ghost Light".)
 * Propaganda Machine: Some characters are convinced that Mistfall is this.
 * Reality Subtext: Matthew Waterhouse sadly knew from experience what it's like to lose an older brother. Twice.
 * Stock Episode Titles: 45 uses
 * Tomato in the Mirror: The revelation that.
 * Ungrateful Bastard
 * Up the Real Rabbit Hole: Of course our universe is the Normal one.