Richard swallowed carefully as he looked at Door's matted hair. This was a REALLY badly thought out decision - He didn't know why he had stepped through the door when the Marquis invited him, nor did he know why the spear that killed the Beast was singing to him even as the Marquis offered it to him. He didn't even want to know why Door was holding a little boy with black hair and a lighting bolt scar.
The Marquis had smirked, handed Richard the spear, ordered both adults (how old was Door?) to follow him. That's when Richard realized that they weren't in the sewers like he'd been expecting, but rather, they were standing in front of identical houses.
"So. This kid's English name is Harry James Potter, courtesy of his In-Betweener-Father. His Fae heritage is through his dear departed mother, and as I'm making sure one of the Fae are taken care of, my debt to them is complete. Door, I've brought you Richard, and Richard, I've brought you to Door - you both owe me, but one of those debts is repaid by Door taking care of the kid until he's seventeen. Do try not to die, Richard, Door." And the Marquis twirled around, disappearing into... someplace.
Richard had forgotten how annoying the bastard was, and how confusing everything in London Below was.
"I don't think I understand. Fae? In-Betweener-Father? How did the Marquis get the spear? What-?"
"Well, remember how I said parts of time were trapped in London Below? The Fae are part of that. Druids, Sidhe, Fae, whatever you call them, lived in Ireland, spread to Scotland and then to England, playing little tricks. Then they started going underground... basically, the Fae are the oldest parts of London Below, but under all of... well... Europe. They have different names in different places; in France they're like the Veela's ancestors... Changelings are Fae children who are simply more suited to the human world, so they replace them with human slaves - you know the old Irish myths, right?"
Richard nodded, pretending to understand the 'Changelings' bit.
"Well, Lily was a changeling, and she remembered the Fae world, too. We met a few times, and she told me about the in-betweeners. See... you know Merlin?"
"Not personally. But I've read books. And Arthur was the more famous one in the books."
"Well, there's a whole community of wizards and witches, and they have little pockets of England squirreled away for themselves, little bits blending in with London Above - like the Leaky Cauldron and the Hogwarts Express - and with London Bellow - like Knockturn Alley. You'll figure it out later. But Lily got married to some In-Betweener called James, and they have little Harry. They also have a big war, I dunno the details, but Hunter killed a couple-a dragons. And. We have to take care of Harry, who's part Fae and part In-betweener until he goes to some school called Hogwarts at age eleven, and we can get him back for the summers, and he comes 'of age' when he's seventeen."
Richard decided he needed either sleep or some Earl Gray to deal with this, and he said so.
"Mm-hm. I agree. Now let's go to my old family house, I'm sure that's a good place to raise a boy. And we need to tell him his Fae name to unlock his Fae powers, but supposedly it died with Lily - his mom. At least, the Marquis said supposedly, so that means he expects us to figure it out. At least there's a letter explaining things. It was written by the head In-betweener, Dumbledore."
And Door slipped into the Sewers through the gutters - without hurting Harry - leaving Richard to follow while awkwardly handling the spear and knife. Well, he did ask for it.