Somehow the napkin that answers them expresses the emotion 'pleased'. You're too kind. Amy, I can certainly provide you with however much you want but I should warn you that it loses much of the effect if served warm.

Gren starts asking Bar to quote prices to buy textbooks - medical, engineering, electrical, mathematics.

Such books would start at about £40 each. The entire list would cost at least £1500, depending on the particular books I choose. Gren flinches at the number. It's almost enough to buy a house! My apologies. I am obliged to charge significantly more than average for books of a technology level higher than your own, especially many years higher.

"I have the Chilling Charm, so I'm fine. How much pocket money do I even have left? Hmm. How much for a case of that stuff?"

"Hmm, Bar, what if I asked the prices for all the same textbooks, also in Gren's money so as to not deal with the finicky conversions and time weirdness all at once, for myself?"

To Amy, Eight sickles, six knuts for a pack of twenty-four.

To Flora, I try to discourage excessive arbitrage. One or two instances is acceptable, but do be aware that I may have to stop if you get carried away. That said, £155.

She returns the forgotten potions book, which is absolutely undamaged. Her tab is now 0.
She quickly converts the £155 to wixen money in her head, just in case it isn't as bad as it sounds, (it's worse) and... thinks about how to cheat.
I need to get the information to Gren's world, not specifically the books. So, if I put them on my tab, and find a way to re-record them... Was there a spell for that? Duplicating, doubling-- aha, the Doubling Charm, she remembers.
That one was a hard one at the best of times. I need my notes.
She summons her notes again.
"I may be able to make temporary copies of any books we get on our tabs, but it's a really hard spell. I've got to read the notes first, of course, as always, and practice on something else a whole lot of times."

She counts. "Uh, I've got enough for a pack of twelve, in that case." She slides the coins over.

"Uh, hey, I will totally knock a hole in the wall and get someone from the government with government money to come here, we don't have to cheat too hard and I can pay you for all the magic stuff. Amy, I bet they'll buy you a year's supply and then some for all the potions and the communication mirrors and cutting runes and so on. Bar says she can drain money straight from bank accounts."

"Ooh, okay. So, will we first check the ley lines or call in someone else and break down the wall?"

"If that happens, I'd like variety, not just the one thing I liked."

"May as well do them at the same time? This is exciting, new magic."

"New magic is very exciting, yes," she says and smiles.

"Alright, let us through to your room, then."

So she stands up and walks over to the door and opens it to a very... Plain-looking and small room. There is a small, dirty window overlooking some kind of town or city. Not much detail is available; It's foggy.

"You'll probably need the shouting spell, to get anyone's attention."

"Sonor-"

Flora grabs her arm and raises her eyebrow.

"Oh, wait, I should probably cast on you, I'm not sure a random voice would be trusted." She sighs. "Sonorous!"

"CHIEF LAWRENCE! THIS IS GREN! I FOUND A NEW WEIRD MAGIC THING! IT'S ACTUALLY USEFUL THIS TIME! IT TOOK OVER MY ROOM'S DOOR, BREAK DOWN THE WALL!"

Aaaaand now we wait.

"I think it might be better to break the wall from this side, this room is pretty small, after all. Does that sound like a good idea? Or is there a chance of the corridor getting blocked, or something?"

"I was thinking of smashing into the room next to mine. We don't own 'em. But going into the corridor will work, too. Can one of you do it? Bar said I have to keep holding the door or it'll stop existing when I quizzed her earlier."

"I wanna!"
She casts a few Cutting Hexes at a wall. There is now a hole in said wall!

There are some confused-looking people dressed like Gren, whose reactions seem to be variations on 'Gren's doing weird things again'. And shortly thereafter, there is a very prim-and-proper older woman and a buff-looking moustached man in very bright uniforms emblazoned 'UDF'.

"Hi, Chief Drill Sergeant Lawrence and Senior Drill Sergeant Hamil. This is Milliways, and these are Amy and Flora. They've offered to sell magic items to us."

"Yup! We sure have! The Neuroi sound really bad."

"We're going to check if you have these things called ley lines in your world. If you do, the items that aren't potions are reusable and Gren can make more potions, apparently."