[A/N Originally written for Yuletide 2013 and published on AO3. Based on the prompt:
"[...]or perhaps something taking place after the existing plot in which they are all interacting again. Maybe de Carabas needs a favor from them this time[...]"]
London Below was filled with dangers and magic, but nothing in Richard Mayhew's adjustment to his new life there was as difficult as the grotesquely literal way that names from London Above echoed into his new world.
Sometimes this was a relatively benign thing — Old Bailey was a nice enough sort, after all, and the Black Friars turned out to be very good chaps once the unpleasant business of nearly dying during the ordeal was done with. However, there were things out there that still gave him the shivers — Night's Bridge, for example, and later, his one visit to Cockfosters had scarred him badly enough that he refused to ever speak of it again, not even when Door teased him about it mercilessly.
After a while, Richard got used to such oddities, and even began to expect them and take them in stride.
And then, one day, Door received word that the Marquis de Carabas needed to meet them, though precisely why he didn't say. The message was delivered (not unexpectedly) by a rat, and specified that they could find him at the Elephant and Castle. Door asked the creature to tell the Marquis they would go to meet him as soon as possible.
Richard had learned by now that if he didn't ask for an explanation of something, it might never even occur to anyone that he might not already know all about it. He didn't ask Door to explain what the Elephant and Castle was, and sure enough, she didn't volunteer any information about it. He felt that by now asking was redundant anyway — he could guess well enough.
They left The House Without Doors (a name which Richard found funny given that Door herself had been in residence there most of her life) and walked for some time through the tangled passages of London Below, until at last at last they came to an isolated building in what appeared to be almost a cavern.
Building on building on building seemed to have been built up all around, sealing up the structure before them so thoroughly that it had been concealed from light and forgotten by the city above for centuries. It was an old Tudor-era coaching inn, whose entry sign proclaimed it "The Elephant and Castle".
The interior proved to have all the amenities one expected in an Elizabethan public house — a filthy floor, crude tables and chairs, a fireplace, and poor illumination provided by candles and lamps.
"This is it?" said Richard, with an air of incredulity as he looked about the room. "It isn't what I had imagined at all."
"What did you expect, Sir Richard?" asked the Marquis de Carabas, who was seated quite near the doorway. "An actual Elephant, and a Castle too?"
"Well, yes, in fact," said Richard.
"Don't be silly, Richard," said Door, who laughed a bit. "It's just a name! Everyone knows that!"
"Well, I didn't," said Richard. "There's a place called the same thing in London Above you know, named after an old pub, but I expected this would be different."
"How would one keep an elephant happy and well fed down here?" said the Marquis. "Really, of all the ideas. Do you think there's an actual W.C. at Water Loo as well?"
"There isn't?" said Richard.
"No, of course not! There hasn't been in almost thirty years, you know," said the Marquis.
"Anyway," said Door, "what can we do for you, Marquis? Your note was rather vague."
"Ah, yes. Well, about that. I was wondering if Sir Richard might be able to help me with something."
The Marquis reached into a pocket and pulled out a small glass container with a worn but familiar label.
"Can you tell me anything about this, Richard?"
"That?"
"Yes, this object. Do you know anything about it?"
"You mean, besides the fact that it's an empty jar of Marmite?" said Richard, with an air of incredulity.
"So you do recognize it!" said the Marquis.
"What's not to recognize?" said Richard.
The Marquis leaned in towards him.
"Can you get me another?" said the Marquis, conspiratorially.
Richard thought for a moment. He hadn't liked being patronized. Perhaps a small prank was in order.
Richard turned his features grave.
"You need," he said, slowly and with a tone of seriousness, "an empty jar of Marmite?"
"A full one, actually," said the Marquis.
"Full!? Why?" said Richard, affecting the air of a man who has just been asked to break in to the Louvre. "Do you know what you're asking for? Do you understand what that stuff is like? Why do you need it?"
"Someone asked me for it," said the Marquis, vaguely. "I promised to get it for someone in exchange for a favor I need for... something else, you see. Never mind about that. Are you saying it will be tricky to acquire?"
"Saying it will be tricky," said Richard, "is not exactly how I'd put it, if I were being perfectly honest."
"But you do know how to get it."
"Oh yes," said Richard, turning away for a moment. "I suppose if anyone knows, I would."
"Er, what, exactly, is a Marmite anyway, Richard?" asked the Marquis, whose curiosity was clearly getting the better of him.
Richard looked straight and hard into the Marquis' eyes.
"Opinions on it are divided, and extreme," said Richard, with a harsh tone, though quietly, as though he also did not wish to be overheard. "Some say it is wondrous, without compare, and seek it out. Others say it is the foulest thing of its kind mankind has ever conceived of. I understand, but I cannot say which, if either, is more true. Anyway, you say it is important?"
"Moderately important," said the Marquis.
"Only moderately?"
"Er, maybe a bit more than that."
"Very well," said Richard. "You'll owe me a favor, of course."
"To the Lady Door—" said the Marquis.
"To me," said Richard.
"Certainly, certainly," said the Marquis. "I would have expected the same."
"Well, I suppose we had better be going," said Richard, standing up. "We'll send word if and when I succeed."
"If?" asked the Marquis.
"Have you ever seen a Tesco, Marquis? Even a small one?" asked Richard.
"Um, can't say that I have, no," said the Marquis, who clearly had no idea what a Tesco might be.
"I may have to go inside one."
Door had developed a worried look during the conversation, but she remained largely silent until shortly after they left the inn.
"Richard?"
"Yes?"
"What sort of creature is a Tesco?" she asked anxiously. "Are you going to be alright?"
Richard laughed, and then gave Door a hug and a quick kiss on the forehead.
"I probably should explain a few things," he said.