"Professor, could you get him one of the charms that let Muggles see Hogwarts?" 

"Certainly, Miss Granger, anything for my most attentive student. Right this way." He sweeps off with a swirl of robes that's a bit too dramatic to not look rehearsed.

Okay, they're following this guy then. It remains a really good thing Cam's not afraid of heights. "This requires going somewhere? Do you not have your wand on you or do some things require extra doodads?"

"It's a necklace. A lot of persistent magic is enchanted objects; it's less likely to come undone that way."

"You should be glad it's a necklace," Harry mutters too low for Lockhart to notice. "Last time he cast a spell on me he got it wrong and I spent the night in the hospital wing."

"Huh. And there's just one around? Who-all comes to visit under typical circumstances?"

"I think all the teachers have a couple? It's mostly people's muggle parents."

"How considerate of them to have this, uh, disability accommodation on hand."

"Guess so, yeah. I haven't really thought about it, all my family are magic."

"I would be interested in pie charts of the demographics here but it is not urgent."

"You make charts out of pie?"

"It's a figure of speech, the charts are circles with wedges of different colors."

"That makes more sense but it's not as much fun."

And here's Lockhart's office! Lockhart presents Cam with a wooden disk on a leather cord and a long-winded story about how he once had to enchant one of these on the fly while rescuing the princess of some country Cam has never heard of.

"Is that some kind of secret magic country," Cam says, donning the necklace, "or the magic name for a country Muggles know by another name...?"

"I believe it's in the area muggles call Timbuktu. What brings you to Hogwarts, by the way? Would you like an autograph?"

When Cam puts the necklace on, the architecture goes from "crap even before the decades of neglect" to "beautiful and very well-maintained stonework". All the walls and doors are in the same places, at least.

"I don't really collect autographs, thanks. I was summoned."

"Professor, we know what Slytherin's Monster is. It's a basilisk."

"A basilisk? Fascinating. Unfortunately I have just been, ah, called away to, ah, a very important conference. I'm sure you'll all be able to handle yourselves without me." He pulls out a suitcase and starts tossing random objects into it.

...Cam looks at the kids because he does not know if this is expected wizard faculty behavior.

Yeah, this is pretty unsurprising.

No, this is very surprising!

"But you're the Defense Against the Dark Arts teacher! You can't just leave when there's a monster attacking the school!"

"Are giant snakes a dark art?"

"The Defense curriculum is supposed to cover protecting yourself from dangerous creatures."

"That's not the point, the point is that Lockhart's a fraud."