When Professor Lupin takes Black out of the room Harry has to fight off the irrational urge to follow them and confront his parent's betrayer.
Instead he forces himself to listen to the terse explanation of events from the purple-haired person. It covers the same things that Charlie had been telling Ron during Black's outburst.
At the end of it Harry doesn't know what to believe. He does know which version of events he'd more like to be true; after all, if Black is innocent then Harry has a family – a little messed up family, clearly, but still better than the Dursley's.
By the time Lupin comes back in, looking harrowed and aged, and raises his wand at Scabbers Harry is basically vibrating on the spot.
A flash of pale blue light engulfs Scabbers and for a second nothing happens. Two seconds. Three. Harry feels his heart drop.
And then, on the fourth second, the rat begins a horrifying, gruesome looking transformation. It is nothing like watching McGonagall switch between her cat form.
But the end result is the same. The rat is a man! Which means that Black is innocent, and that they can prove it!
Just as this realisation floods Harry with warmth, an ear-splitting scream comes from the spare bedroom.
Lupin moves quickly from his position in front of the rat-man but Harry gets to the door first.
"Can I go?" He blurts.
Lupin looks wary but, after a short pause and glance at the frightening man in the corner, nods. Harry gives a wide smile and turns to leave the room; in doing so he catches sight of Ron and Hermione's scared faces. They haven't changed opinion on Black quite as quickly as he has. But this is personal; Harry's sure they'll understand.
Pushing the door wide Harry is acutely aware of Charlie Weasley's presence and wand even as he hurries to Black's side. Conversely, Black does not seem aware of anything at all, barely managing to make eye-contact with Harry.
"James." He says again.
Harry bites his lip. He's used to being compared to his father but Black isn't just remarking on the resemblance. And that can't be right. Black can't be insane. They're going to be a family.
"I'm Harry. Sorry."
Black's eyes narrow but then clear. "Harry." He says softly. "Why are you sorry? I'm the one who should apologise." He shakes his head roughly, like a dog shaking itself dry. "I do apologise. I'm so sorry Harry."
He says Harry's name like it's a miracle.