"Who, Pettigrew? He needs to have a trial."

(Pettigrew is pretty sure people die in space and isn't sure why the weird terrifying winged person would pick that method of killing him and doesn't want to ask.)

"After that would be fine. I can only assume wizards are not members of the United Nations but you could still, like, consider their human rights declarations a loose guideline. I assume if wizards could traverse the vacuum of space you'd be doing it, I don't have to make a space station that mechanically relies on electronics for its air supply if I do a chemical or autoponics version in case him being a wizard messes up the circuitry, I guess it'd be solitary confinement but he obviously doesn't rely very heavily on charming conversation because he has been a rat for more than a decade. Unless rats can talk. Can rats talk? I can visit a pet store."

That was a whole bunch of words McGonagall doesn't know and concepts she's never heard of and she needs to take a moment getting on top of it. "Are you saying you intend to abscond with him in the event that he's sentenced to Azkaban? That would almost certainly be illegal, though I'm not sure whether they would call it aiding a fugitive or kidnapping. And admittedly it's also unclear whether anyone would be able to stop you."

"Well, are you saying you plan to have him tortured?"

"A fair trial for Pettigrew is the best means I am aware of to get a fair trial for Black. It seems likely, at this point, that the latter will be exonerated and released, and the former imprisoned."

"And tortured."

Somber nod.

"I really don't think that's the sort of problem best addressed by making a very sad face while it happens anyway."

"I don't have any other options. Even if I wanted to let Pettigrew escape, that would leave Black imprisoned."

"I concede I do not know what degree of hilarity of a legal system you are working with here but not getting a guy tortured may require more than five minutes of thought."

"Well, the DMLE agents will have to walk here from Hogsmeade; I'm happy to spend the intervening time explaining our legal system."

"Uh-huh."

McGonagall starts explaining the British wizarding legal system like someone who explains complicated things for a living, with a focus on "How did Azkaban start to be a thing and why is it so hard to get rid of."

There are three main parts to the problem. First, containing wizards is hard. They can't do much more than muggles can without wands, but any solution for keeping them alive and preventing outside people from breaking them out requires guards with wands, and then you need to prevent the prisoners from stealing wands off the guards.

Someone a long time ago decided to solve this problem with dementors, but that led to problem two: it turns out that confining a bunch of dementors in one cold damp place with a steady supply of victims causes them to breed, and now Britain has way more dementors per capita than anywhere else. There's no way to kill them, and releasing them would be both dangerous to the general population and likely to cause an international incident over the odds that some would wander across the Channel. 

Problem three is that the government is corrupt and rarely does anything that doesn't benefit them personally, and even if they weren't there's a sizeable number of people who think prisoners are bad and therefore prisons should be as awful as possible.

"Can wizards traverse the vacuum of space? For that matter, can dementors?"

"An interesting question. Muggles have been to the Moon, so the question is whether wizards can improve on their methods. If any have done so, they haven't made it public knowledge, but I suspect it could be done by a sufficiently clever and determined wizard eventually. As for dementors, I doubt one has ever tried. They feed exclusively on people."

"See, I can super traverse the vacuum of space so I am curious if my idea of stranding the dementors in space and/or implementing Wizard Space Prison works. But actually come to think of it I don't have a specific investment in this one guy and there are presumably other people in Azkaban also?"

"Yes, dozens. And even if you don't find a prison solution, there are wild dementors in other countries. I expect you'll want to strand at least those ones in space?"

"That is currently plan A."

"I hope you're thinking of putting them on a particular planet, rather than simply adrift. They move by gliding; they might be able to return to Earth if not subject to gravity somewhere else. And what is the rest of your plan?"

"I can put them on, say Mercury, nobody wants to live on Mercury. Or in a space station. My plan is not very firm at this time containing as it does many question marks about dementors, political realities, etcetera."

"Do feel free to ask me any questions you think of. While of course I would never assist with anything illegal, I'm always happy to provide new residents of magical Britain with information about our society." 

(Pettigrew has no opinion on any of this and in fact seems to have fainted.)

"A lot of it might hinge on how disruptive smaller-than-Hogwarts amounts of magic are to electronics, do you know about that?"

"The second most warded place in magical Britain is Diagon Alley, and people who live there can use electricity, so I believe it's only a problem here unless your devices are especially delicate."

"I will try to plan around particular robustness of devices but maybe I should try using a computer in... uh... diagonally."