She drinks the coffee, slowly, and with her eyes locked on the fire over the top of the cup.

The flames shrink to the size of a bonfire, then a campfire, then a very angry candle, and finally dwindle into nothing. Not even ashes remain of the diary.

"Can I get you anything else? I wasn't expecting this to take that long." He wants a hot dog so now he has one.

She brings the broom down, dismounts, leans on it like a walking stick for a moment before slinging it over her shoulder and setting off toward the castle at a noticeably slower stride than before. "Perhaps a cup of tea? Cream, no sugar."

"Oh, right, this is Britain." Tea earl grey hot.

"Thank you. For the tea and for your assistance earlier. Miss Weasley should be safe now." She drinks the tea while they hike back to Gryffindor tower, vanishing the empty cup when she's done and pausing only to grab a portrait of an armored knight off the wall, explaining to it that it needs to fill in as Gryffindor password check for the rest of the term.

"Interesting security system you have."

"The Founders came up with it. Ravenclaw uses riddles, but the other three all have variants on passwords. Though Gryffindor is the only one which enforces it with a portrait."

"Does the portrait add much to the security? Do they recognize the students or something?"

"They can learn to, though there are so many forms of magical disguise that the password is still very important. The main benefit is that they move their own frames, which makes it harder to sneak in behind someone else."

"Oh, cool. I guess passwords probably work all right as long as computers don't."

"I don't see the connection?"

"Uh, when computers work a bit better than they probably do in this era they get good at trying a lot of passwords very fast and it makes it important to have heftier security but this is probably fine for your use case except when giant snakes bypass the password mechanism entirely."

"I'm not sure how anything could try passwords faster than the portrait can hear, but as you say it's unimportant. The Basilisk was the first security breach we've had in some time." She installs Sir Cadogan, lets herself and Cam in, and goes to untie Ginny Weasley where she's asleep on a couch.

The ropes vanishing is enough to wake her up. "Hmm? What--what happened? You wanted to look at the diary, and then . . . How much trouble am I in?"

"None anymore, as far as I can determine. You were being controlled by the diary, but it has been destroyed and the effects of the curse should fade quickly. Nonetheless you should see Madam Pomfrey."

She looks searchingly at Ginny. "How much do you remember about what the diary was making you do?"

Ginny answers, in a whisper, "I was attacking people . . . Justin and Colin and Mrs Norris and those roosters--I'm gonna be expelled!" She bursts into tears.

"There, there," says McGonagall a bit awkwardly. "You're not going to be expelled, it wasn't you doing it. But can you tell me where you got the diary?"

"I don't know. It was inside one of my textbooks when we got home from buying them."

"...do you shop at an evil bookstore?"

"N-no? It was the used section of Flourish and Blotts."

"Maybe they keep records on who donates them stuff or something. Probably not though..."

"And they probably get a lot of copies of A Beginner's Guide to Transfiguration."

"I take it you're interested in helping trace the book? Would you like an empty classroom to work in?"

"I couldn't conjure the book," Cam points out. "I can see if surroundings work though, sure."

"That could work. Miss Weasley, do you remember the date you bought your books?"