Chapter Text
"So, it's infinite, but it's not infinitely infinite," is the very unpromising start to Charles's tutelage in the workings of the personal pocket dimension within his backpack.
"I'm not following so far," Edwin says flatly.
"Right. First, the easy bits," Charles beams, undiscouraged. "This back pocket here is only about three times as deep as you'd expect. Has two snap buttons, so if you unbutton left to right, you get one space that size, and if you unbutton right to left, you get a second different space that size. This is where I keep a lot of lobbables to hand, like your emergency potions, road flares, and watch out for that one all the way to the right, that's a flashbang and it's already armed."
Edwin can't help shuffling back. "Why?"
"Never know when you'll need 'em right away! Remember on the Case of the Temperamental Toybox, the ventriloquist dummy was biting my hand and the Monkey-Do had its arms wrapped round my mouth, so when I fished out my flashbang I couldn't pull the pins until I managed to step on them?"
"Yes, Charles, I vividly remember the time you nearly lost two fingers to a half-unstuffed Sailor Jim figure," Edwin says waspishly.
"Well, and so, these ones in here are already set to go, just need to pull 'em out and throw 'em at your cursed toybox or what have you. Everything in the bag stays just exactly the same for as long as it's inside, so we may as well take advantage and keep things primed."
"And what if one of these live bombs were to roll out while you're fetching out a road flare?"
"Thought of that, didn't I? I stitched in a loop I have to flip up with my thumb to get it out, otherwise it's going nowhere."
"Oh, well, if there's a loop," says Edwin.
Charles rarely glares, as such, but there's a more-in-sorrow-than-in-anger look he sometimes levels at Edwin which honestly feels far worse than a mere glare. "There is a loop, and it works. Never been blown up accidentally yet, have we?"
"It's just a bit disconcerting to learn you habitually carry live ordinance hanging casually off your shoulder, Charles," he can't help pressing his luck. "Don't be so eager to have weapons readied that you risk them going off and doing you harm."
Charles softens a bit at that. "I'm fine. I know what I'm doing. Now let's just get you up to speed as well, yeah? With this back outside pocket, both the spaces inside have the same stuff, it's just two sets so we have extras. You only need to remember that if you run out of something from here, you can button it back up, unbutton it from the other direction, and there's more in the other space."
Edwin rubs his temples. Ghosts can't get headaches as such, and yet. "Show me?"
"Left button, right button, here's the test tube with your smoke potion," Charles tugs the beaker out and sets it aside. "Say I take it out and lob it, but I miss."
That scarcely ever happens— Charles' pitching arm has been remarkable from their earliest acquaintance— but Edwin forebears to comment.
"So I do up the snaps again, and undo them right button then left button, and there in the exact same place, another smoke potion!" There is indeed a beaker there, identical to the one Charles set aside.
"And these are the easy bits," says Edwin, forlorn. "What about the main part of the bag?"
"Yeah, there is a bit of a trick to that," Charles admits, speedily buttoning and unbuttoning the perplexing outer pocket to return the first smoke potion to pride of place. "Left buckle then right buckle, then you flip up the top. Move the stopper all the way down these strings, has to be all the way down, that's important."
Edwin received twelve years of the best classical education the public schools of England had to offer in his time. In the past few years, he has taught himself runic alphabets and dozens of magic sigils, as well as enough Aramaic and Enochian to become adept at complex incantations in both languages. There is no conceivable reason he should be muttering to himself Left buckle, right buckle, stopper all the way down the strings and still feel he's missing something important.
"Then you open the top and put your hand in, only to about here," Charles demonstrates, his hand poised just inside the mouth of the bag. "And you can kind of feel there's nine different... areas. I dunno, nooks? Zones, maybe. You need to know the one you want, you can't reach into two at once. I think that's what happened that time you felt like it yanked you about."
"If I hover my hand exactly there, I'll feel nine different invisible zones, of which I can only reach into one," Edwin repeats. At Charles' nod he throws up his hands. "Charles, I've seen you reach straight into that bag a thousand times, there's no hovering and feeling around for zones!"
"Well, I don't have to, do I, that's what all the practice was about," says Charles. "By now I just know where they are. And when I go into one," he thrusts his arm into the backpack, "this one expands, the others go away, and this one becomes its own separate infinite space. That's what I mean about how it's not infinitely infinite— it's not one big infinity, there are compartments, like. Except once you're in this main part of the bag, they're not physical compartments, they're sort of intuitive regions you tune into."
Edwin pinches the bridge of his nose. "There are nine variably perceptible infinities in the main body of your backpack."
"Well..." Charles hesitates.
Edwin amends, "There are eighteen variably perceptible infinities, because if you undo the buckles the other way 'round, you get a different nine?"
Charles chews his lip. "Um."
"Charles, do you get yet another set of nine for every position of the stopper?"
"You get another set of eighteen for every position of the stopper."
"I surrender," says Edwin, lest he begin tearing at his hair. "Charles. I am tremendously impressed and pleased for you that you have mastered this frankly insane spatial nightmare. Please just show me how to fish my books out of whatever finitely infinite, intuitive, invisible compartment-region-area-zone contains them, and I will gladly leave the rest to you."
"All right, mate," Charles pats his hand consolingly. "Let's take a breather, maybe spin through a good old Father Brown mystery to get your head back in the game, and I'll show you it. Your books are in the easiest spot to reach, I promise."
"Merely left buckle, right buckle, stopper at the end of the strings and perceive the appropriate zone?"
"'Zactly. It's right bang down the middle. Bet it won't take you more than a year to get the way of it."