Harry made it up to the Study Session (as he'd taken to calling it in his head, as it seemed more than borderline disrespectful to call it Dumbledore's Army when Draco Malfoy was attending, alongside the rest of the Junior Death Eaters - the rest of which, Harry hoped devoutly, weren't actually branded. Yet.)
That last word had Harry Potter striding into the Room of Requirement with a scowl fit to sit on Snape's face. He only barely glanced at Boot and Connor, both of which were going to teach the class in tandem.
Well and good, Harry thought, though he wondered what they'd be teaching. He didn't have many classes with them, and they didn't stand out all that much in the classes that he did have with them.
As everyone filed in, Harry's eyes flicked to the few Slytherins that he'd marked as not knowing a Patronus at all. He wondered, idly, if there was something he could do about that. Blinking, he rethought that - it would have to be something real. Not something faked, and that meant something more or less permanent. He probably wouldn't be doing anyone any favors befriending Slytherins - the rivalry between the Houses wasn't something that Malfoy and Potter'd made up in some sort of joint pact, after all.
What Boot and Connor had cooked up wasn't something Harry would have thought about instinctively. It was the uses of Transfiguration in battle situations. And not the way Dumbledore had fought, using high powered (and very difficult) Transfiguration to set up the other person.
No, this was low powered transfiguration. But that was why it worked. Spelling terra firma into mud, transfiguring a layer of muddy snow into ice (still hidden under a delicate layer of snow). Even something as simple as making boots lighter. Harry'd smirked as he'd transfigured a glass sphere into lodestone. Yelps from other people were heard as various trinkets, rings and other bits started to fly towards the ball. When Harry saw someone's knife flying at it, though, he thought better of this plan, diving for cover.
It took about three minutes for everyone to have their stuff lifted out of their pockets - both from pressing closer and turning towards the sphere.
"What is that?" Pansy snapped, less angry about her stuff being stolen (and there was a lot, including a very pretty looking laquered compact) than about not knowing what it is.
"It's a thiefstone." Harry Potter explained, "It does just about what you see here."
"Harry!" Hermione said, putting her hands on her hips.
"Odd," Malfoy said, studying the debris... "There's a pattern to what's here and what's not. It can't just be metallic, or our money would have come too." Draco Malfoy's silver-gray eyes flicked up at Harry, who was trying to defend himself from Hermione, who was using her glare (and elbow) to enforce her will.
Malfoy, gaze darkening at being ignored, simply walked up behind Granger (well, more stalked, really...), and lifted her off her feet, depositing her about two feet away from Potter. Hermione actually gave Malfoy a hiss before she leaped back over to Harry.
Malfoy tilted his head at Crabbe, who came over and lifted Hermione off the floor - again. Her kicking feet were trying for his groin, but he had also been watching Malfoy. He did what the slighter, shorter, frailer boy couldn't - put Hermione in a Princess Carry, and held her there.
Out of perhaps sheer shock, Hermione was silent. Harry wanted to cringe. Whenever there was silence around Hermione, it boded poorly for later.
"Why didn't it take our money?" Malfoy asked, "What's so special about what it did take?"
"Magnetism." Harry Potter said shortly. "It's a property that the Wizarding World doesn't study well or often, but the muggle world practically runs on it."
"The Muggle wordl runs on stealing things with thiefstones?" Goyle asked in a state of perpetual confusion, "Seems a bit unworkable to me."
Harry Potter shook his head, smirked a smile, and said, "Just ask Hermione if you want details." Behind his back, Malfoy rolled his eyes, making motions like pulling taffy to indicate that you'd receive alll the details you never wanted.
[a/n: Harry wasn't going to explain at all, and Hermione knew it.
Draco may like Hermione, but he's still an enormous prat.