Pick an episode (or series) that your character wasn't in and imagine they are - either replacing one of the characters in it, or just add them. Then re-write the episode or pick an event from it to re-write.
“I still do not understand why you need an assistant.”
Leela was standing by the TARDIS console with her hands on her hips, and the Doctor’s valiant attempts to ignore her were falling short. His companion was annoyed and confused, and part of her still wished she’d chosen to stay on Gallifrey with Andred. It probably wasn’t the best time to aggravate her, but playing a half-hearted game of chess against K-9 was so much easier than arguing with Leela. He’d been walking on eggshells since leaving the Capitol, and the trip to Halergan 3 hadn’t been particularly relaxing.
They should have been able to spend a week or two sunning themselves and playing in the sea, but, instead, they were off on a quest, and the fate of the universe was at stake.
Or something like that, anyway. It was a wonder the universe survived at all, since it seemed to need saving every other day at the moment.
“I rather think the White Guardian wants me to take another Time Lord with me. To keep an eye on things.”
“To keep an eye on you, you mean,” she said, rather astutely, “They will not be able to protect you!”
“They aren’t supposed to protect me. They’re supposed to help me.”
“Protecting you does not help?”
“Well, yes, of course it does...” he began, and she interrupted sharply.
“Then why do you need an assistant?”
“Because, well, because it will be a difficult and dangerous quest, that’s why…”
“Am I going to have to protect her, too?”
“I expect so. They aren’t very practical, the Time Lords, are they?”
“I did not think I was practical,” she replied, glancing down to survey her ragged animal skins and bare legs. She certainly didn’t look practical, and was finally starting to understand why she attracted so many strange looks during their various excursions.
“But you can look after yourself,” said the Doctor, and Leela smiled.
“Perhaps one day you will be able to do the same?”
It was the Doctor’s turn to smile then, but, before he could respond, a familiar metallic voice cut across their conversation.
“Master, Mistress Leela…”
“What is it, K-9?” the Doctor asked, glancing sideways at his chess partner.
“The new assistant has arrived.”
Very slowly, they both looked up.
There was a woman standing in the doorway. She was tall and striking, dressed in a long (and beautifully impractical) white dress. The Doctor stared at her for a moment, thoroughly stunned, before glancing sideways at Leela. She looked as astounded as he felt, and the Doctor couldn’t decide if that was a good thing or not.
“My name,” the woman announced, “Is Romanadvoratrelundar.”
“I’m so sorry about that,” said the Doctor, straightening up with as much dignity as he could muster, “Is there anything we can do?”
Leela, who had moved effortlessly to stand at the Doctor’s side, stifled a laugh, and Romanadvoratrelundar turned to face her.
“You must be the…err…savage,” she said, wrinkling her nose in distaste and ignoring the Doctor’s frantic headshaking.
“My name,” Leela growled, “Is Leela.”
“Well, ‘Leela’, I believe your presence is no longer required…”
“Why not?” Leela interrupted sharply, “I am going to have to protect you, too.”
“I hardly need protecting…”
“Fine!” Leela snapped, “Then I will leave you to die!”
Romana had the good grace to look flustered, if not exactly apologetic, but, unfortunately, it was far too late. The Doctor sighed, and Leela stomped angrily out of the console room.
It was going to be a long trip.