The one where you are the companion!
It's a fourth wall breaker special, much like "A Fix with Sontarans" before it, so draw your own conclusions as to its canonicity.
The Doctor has dropped off Rose at an ABBA concert, and since the Earth is being attacked by a Graske, he needs a temporary companion. An Adventurer Is You!
The Graske first terrorizes a regular English family during their Christmas celebration, then hides out in Victorian London for a bit. The Doctor connects his sonic screwdriver to your remote and asks you to help him track the creature down. But first, you get to help him fly the TARDIS.
You eventually sneak into the Graske base, unlock its doors, and find a lot of Human Popsicles (and some alien popsicles) in pods. One of them, a Slitheen, breaks free and starts chasing the Graske, and you have to make a choice... do you teleport all the people back home, or do you freeze them all?
Once you've saved the day, the Doctor happily thanks you, and tells you he might even pick you up as a proper companion someday. (Also, he warns you not to switch to ITV. The galaxy might implode.)
- An Adventurer Is You
- An Ass-Kicking Christmas: You save Christmas from the Graske.
- Christmas Episode
- Disappointed in You: The bad ending has The Doctor admit he's not happy with how you preformed as his companion.
- Full Motion Video
- Gameplay Grading: The Doctor grades you at the end depending how well you do in the game and what your final choice was.
- Multiple Endings: There are two different endings, depending on how well you do and what choice you make at the end:
- The Good Ending: If you make all or most of the correct decisions, The Doctor will happily thank you and tell you that you're ready to become his companion in the future.
- The Bad Ending: If you keep screwing up and/or make the wrong final choice, The Doctor, disappointed, will tell you that you are not ready to be his companion. However, he believes that one day you could be, and encourages you to try again.
- No Fourth Wall: Apparently The Doctor is aware that people have been watching his adventures.
- "Not Important to This Episode" Camp: The Doctor's dropped Rose off at an ABBA concert in the '70s.
- Oh, Crap!: The Doctor's reaction to the Slitheen escaping.
- Only Smart People May Pass: The Graske security system is a series of puzzles. The Doctor decides they must have a thing about porches.
- Something Completely Different: You play as the Doctor's companion.
- That Poor Cat: The Doctor warns you not to let the cat sit on your now-sonic remote. Might end up badly.
- Take That!:
- Apparently switching to ITV could destroy the galaxy.
- The Doctor grimaces after mentioning ABBA.
- Tech Demo Game: Showcases the BBC Red Button system.
- Victorian London: The Graske are taking people from throughout Earth's history.
- What the Hell, Hero?: The Doctor is not happy with you when you screw up. He's more forgiving with the first major problem, spotting the imposter, but after that if you make the wrong choice he will not hold back. Screw up enough times and The Doctor at the end will point blank tell you that you are simply not ready to be his companion.