Doctor Who: Every Modern Companion's DEFINITIVE Episode

Belinda is a slightly frustrating case in terms of this list, because, let's be honest, The Robot Revolution is the only story that feels it's written specifically for her character, and is therefore my only real choice. Everything that follows, particularly across the rest of the season, though this has never been explicitly confirmed, is clearly written for Ruby or a 'TBD companion' with some Belinda dressing sprinkled in at the last moment. This isn't the most remarkable episode, and there are some very debatable writing choices, especially in the episode's climax, but what it does do supremely well is paint a very promising picture of the companion Belinda is going to be. Sadly, this isn't carried through the series, but in isolation it's great stuff. 

The Robot Revolution clearly establishes who Belinda is and what drives her. She is not the adventurous type, waiting to be swept off in adventures, she will not be wooed by The Doctor's promises of universal travel, and more than anything, she's looking to return home ASAP. She is a nurse with a defined ethical code, more concerned with tending to the injured than partaking in any 'traditional heroics', going so far as to (fairly) take issue with the Doctor scanning her without consent. She has a sense of humour, but chides the Doctor for not taking life and death scenarios seriously enough and often talking over people's heads. The bones of a very interesting dynamic are laid down here - one that breaks from the NuWho norm by having an 'unwilling companion'. Why on earth they didn't stick with this, I'll never know. 

Whilst it doesn't do it overly well, the episode does at least connect directly to Belinda's own past, and this is the only time the series bothers to do this. RTD introduced a companion that had the potential to be a classic, hired a cracking actress to play the part, then did absolutely nothing with her, made her play second fiddle to Ruby, gave her scraps of someone else's story, and then character assassinated her by giving her a 'happy ending' that robbed her of her autonomy and gave her a child without consent - remember earlier when I mentioned this being one of Belinda's core principles? 

Rant over. This is what happens when the writing is so bad I don't have a proper option.