"Ron Weasley," says Ron Weasley, suspiciously.

Messy hair kid looks like he's found a bush that grows chocolates and is debating the wisdom of eating one. ". . . Harry Potter."

"Well, nice to meet you all - Weasley, Potter, good old names. Granger I haven't heard, but I must say I like it. Weasley, though - how close are you to Septimus?"

"My granddad? He's fine, I saw him last summer, why do you want to know?"

"Oh."

Edmund looks somewhat poleaxed.

"He's my brother's friend. Um. This seems to put forth a hypothesis."

"Oh, of course--but I've never heard of anyone going that far all at once--we should tell professor Dumbledore or professor McGonagall."

"You think he's traveled in time? Like on Doctor Who?"

"Blimey!"

"Um. Yes, let's talk with Dumbledore, I like to think he'd remember my siblings but he'd certainly remember working with my uncle for several decades. May I ask what year it is, this morning it was 1940."

"1993. Wow, there's a lot of history you need to hear about."

"But we should bring him to Dumbledore first. I know where his office his." 

"Lead the way. Is he still teaching Transfig?"

"No, he's the headmaster now. Professor McGonagall teaches transfiguration."

"Wow. Headmaster Dumbledore. And - you don't mean Minnie McGonagall? Some other, less frightening namesake, maybe?"

Harry and Ron both make a sort of shocked sporfling noise at "Minnie."

"No, I think you're thinking of the right one."

"Did she already know how to turn into a cat fifty years ago?"

"Wow. No, but she was very quick with a Bat-Bogey Hex if she thought someone deserved it. Her sense of justice was very keen. Girl lost a lot of House points for vigilantism."

"McGonagall, losing house points? Things have changed."

"It sounds like she had good reasons." She sticks her hand into what looks like a broken bit of stonework and pulls; the section of wall folds out into a doorway. "Do you have any idea how you could have come forward in time? What were you doing when it happened?"

"Um, I went through a doorway that hadn't been there before... which admittedly sounds like a great way to get dumped in the lake but Hogwarts has always been pretty nice to me, so I thought it was worth a try."

"At least it wasn't a three-headed dog?"

"Honestly I think it might be worse. Unless it turns out Dumbledore can send you back."

"A three-headed dog! Really?!"

Not engaging with that statement, Granger, nice try.

Ron launches into a description, complete with dramatic hand gestures. "And we had to sneak past it to save the Philosopher's Stone from--"