"Sufficiently complicated ones can go on for days, especially when there's confusion over how the law applies, but this pair should be done today unless something even stranger comes to light."

"Yeah, I'll come."

"Alright then. We can go to Diagon Alley after."

Getting there first involves walking to the edge of the grounds, and more relevantly the edge of the wards. 

Maybe it does for people who can't fly.

Lupin gives him an envious look and meets him at the front gate with its statues of winged boars. "Now we apparate," he says. "I take it you haven't done this before; it can be a bit disconcerting."

"Disconcerting how?"

"It feels a bit like being squeezed through a very small tube."

"Wow, okay, thanks for the warning."

"If you'll just grab my arm here, we'll be off."

It feels a lot like being squeezed through a very small tube, and then they're in a twisty little alley.

"What a bizarre sensation. Thank you for the lift." He puts his coat back on.

They step out of the alley into 1990s London and Lupin leads the way into a red phone booth with a broken telephone. He pokes the phone with his wand and a recorded-sounding voice says "Welcome to the Ministry of Magic; please state your name and business."

"Remus Lupin, witness in a trial; Campbell Swan, watching a trial."

The phone booth spits out badges for both of them and the floor starts descending like an elevator.

...Cam makes himself a little lanyard to put the badge on rather than stab his snazzy leather coat.

"I don't expect anyone will ask about your clothing choices, but if they do, just say you had to do something in the muggle world this morning."

The phone booth lets them out into an atrium with people coming and going via several large fireplaces, watched over by a giant statue of two humans, a house-elf, a centaur, and a different species of pointy-eared miniature humanoid, the latter three making stupid faces. Paper airplanes flock overhead, making clearly deliberate navigation choices and occasionally hovering. Lupin leads the way to an elevator and they make their way down, accompanied by some of the airplanes and a couple of bureaucrat types holding stacks of parchment.

Cam squints at an airplane to see if he can read any of it without unfolding it.

It's a memo from Albertius Berntwhistle to Caranthia Mortimere re: fire crab import taxes, but the actual content is stuck down the folded bit.

The elevator stops a couple times to let people and airplanes in and out, and then gets to Cam's and Lupin's stop: a hallway with a series of courtrooms. Black's and Pettigrew's trials are in the big one at the end, and there's something of a crowd converging on the back door to the audience section. Apparently a mass murderer possibly being innocent and a dead hero possibly being a mass murderer is exciting news.

Cam elects to acquire an anti-paparazzi scarf when he observes that their cameras use flashes, and follows Lupin in.

For the most part the cameras are pointed downward at the middle of the courtroom, where a couple of stone-faced people in matching robe-uniforms and a witch with a folder of parchments are leading a man who's presumably Sirius Black to a chair with chains on its armrests. He looks greatly the worse for wear: thin, pale, with a thousand-yard stare to rival any soldier's. He walks slowly to the chair with arms tucked close to his body, staring around like he's not exactly surprised at anything but is having a hard time believing it. The witch takes up station next to the chair, and the two officers retreat to the back of the room.

The witch in the judge's chair flicks her wand and the sound of a gong ripples through the courtroom. "This court will now come to order for the trial of Sirius Black on the charges of two counts of accessory to murder, one count of accessory to attempted murder, twelve counts of murder, and one count of flagrantly public magic. Amelia Bones, head of Magical Law Enforcement, presiding."

The prosecution goes first, in the form of another wizard with another folder of parchments that he clutches like a talisman. He goes over the story many people here already believe: Sirius Black was the Potters' secret-keeper, betrayed them to Voldemort, and when Pettigrew cornered him to confront him about it he blew up the street, presumably trying to get Pettigrew but only succeeding at killing twelve muggles. He apologizes for the lack of eyewitness testimony, but it's been twelve years and all the eyewitnesses would have had their memories wiped anyway.

Then the defense attorney takes a turn. She starts by calling in a mediwizard to testify that Black was in Azkaban for eleven years and only released to the hospital a couple days ago, and despite his very promising recovery is still getting the hang of holding a conversation, and there's no way he could be able to throw off veritaserum, at which point Black formally consents and requests to testify under the influence. The prosecutor has token objections, which Bones ignores, and soon Black is explaining the whole story in a magically compelled monotone. Apparently the Potters had worried about Black getting captured, and switched secret-keepers without telling even Dumbledore. When Pettigrew betrayed them, Black tracked him down and yelled at him incoherently until Pettigrew blew up the street and escaped as a rat. The prosecution asks why Pettigrew didn't surface for the following eleven years, and gets the admission that he probably feared Black's vengeance as much as Voldemort's, but wanting revenge isn't illegal and Black is released to the custody of St. Mungo's.

Pettigrew, of course, does not request veritaserum, but Black's testimony is admitted after some haggling. Lupin spends much of this section white-knuckled, but Pettigrew doesn't decide to bring up the lycanthropy issue. He looks like he would try bolting out of the room if it weren't for the guards and the fact that the chair came to life and grabbed his arms. He gets convicted of everything he did and sentenced to life in Azkaban, at which point he promptly loses consciousness and needs to be levitated out of the room.

Cam takes notes and follows Lupin out when they're all done.

Lupin is silent and subdued the whole way back to the Atrium. 

"You wanted to go to Diagon Alley? We can take the floo from here."

"That works for me. Where does Black wind up at this point, do they just turn him loose with the magical equivalent of a bus ticket?"

"Once he's more recovered from the dementor exposure, yes. He'll have inherited his parents' house by now; I suppose he'll move in there. What a strange thought. And he'll want to see mister Potter; he was his godfather . . ." he trails off again.

"Does Harry know that?"

"Not yet. I wanted to be sure he'd be acquitted first. I'll tell him this evening, if Professor McGonagall hasn't already. Have you ever used a floo connection before?" They're almost at the front of the queue for one of the fireplaces; people are taking little packets of powder out of a basket, tossing them into the fire (which turns green in response), then stepping into the flames, saying various locations, and vanishing.

"I have not! Is it as straightforward as it looks?"

"Pretty much. Just make sure to pronounce your destination clearly and don't try to get out of the fireplace until you come to a complete stop. And keep your arms tucked in so you don't bang your elbows."