She looks at him like this is probably a trick question, but says, "Ice cream . . . would be . . . nice?"

He gives her a little bowl of chocolate ice cream with caramel sauce.

She takes it, peers at it, and eventually deems it probably non-hazardous enough to eat a spoonful, and then another. That might be a hint of smile.

"Thank you."

This appears to have earned him some more metaphorical points with McGonagall. "Do you have enough to work with from here?"

"Think so. Obviously I won't recognize any bad actors who turn up so I'll need someone to identify them from models."

"Of course. Would you prefer to work in our library, or an empty classroom? I can't leave you in here unsupervised and I need to take Miss Weasley to the hospital wing and then deal with the probably former Defense Professor. Oh, and I'll need his wand back."

"Classroom is fine. What's going to become of his wand?"

"I'm going to return it to him, probably right before evicting him from the castle. Only extremely serious crimes would justify keeping it from him."

"...he erased a child's memory. With the wand, I'm not suggesting it as a punitive, it's a preventative. Is this like suggesting taking somebody's hand off in wizard culture or something?"

"Almost any wizard would rather lose their hand than their wand, even if hands weren't more easily replaceable."

He sighs and hands over the wand; its ice has long since melted.

"Thank you. If it's any consolation, he will lose his reputation, and knowing him that will be almost as harsh." She pockets the wand and shows Cam to an unused classroom with a handful of desks and chairs pushed up against the wall.

Cam sets about tracing the evil diary's steps.

The used bookstore turns out to be blameless. Ginny's textbook doesn't acquire its evil passenger until a couple hours after purchase, when an extremely sinister-looking blond man sticks his hand in the cauldron, inserting something that can't be conjured but crushes the right amount of pages.

Cam picks up the model of the sinister blond man and goes looking for McGonagall.

She's in her office, pulling her head out of a small head-height fireplace on the wall. The fire in it is bright green, and goes out as she steps back.

"Hello, Mister Swan. Was your investigation successful?"

"This guy, whoever he is, tucked the evil diary in her textbook." He displays Tiny Evil Guy.

McGonagall sighs. "Lucius Malfoy. Utterly immoral, and politically untouchable. Still, I confess myself surprised that he would do such a thing while his son is a student here."

"It's questionable on a lot of levels. What's politically untouchable about him, is he like Wizard Emperor?"

"No, but he's been making generous political donations for years, and gotten away with worse crimes with more or at least more legible evidence. . . . Perhaps I should give you an overview of recent British wizarding history. I'm beginning to suspect the involvement of He Who Must Not Be Named."

"Why must he not be named, does his name make people's ears bleed?"

McGonagall looks slightly put out by the levity, but continues, "He Who Must Not Be Named is a dark wizard, convinced that those of "pure" wizarding blood are superior to muggles and to wizards with muggle ancestry. He and his followers terrorized wizarding Britain for years, and came perilously close to overthrowing the Ministry of Magic. Eleven years ago, he attempted to kill the infant Harry Potter and was instead somehow incapacitated. Malfoy was one of his followers. He claimed to have been controlled by the Imperius Curse, a powerful dark spell that lets the caster overrule another's will, but it is widely believed that he went willingly. And He Who Must Not Be Named was a parselmouth. Between the involvement of Malfoy and the basilisk, I believe he is somehow behind all this."

"I guess that's a reasonable guess given those clues."

"Didn't Miss Weasley say the spirit went by Tom Riddle? I knew a Tom Riddle at school . . . a Slytherin, and rather nastily charismatic. I don't suppose you could discern his current whereabouts, or whether he's still alive?"

Tom Riddle and surroundings?