After the meeting, Marisa immediately left after just a slight glance at Leo. "Just going to the library," she said, "thought I might catch up on some homework."

Leo followed her, and before long they were hidden in one of the quieter sections: a set of books on Ancient Runes.

"Well?" asked Leo.

"I overheard Potter talking to Weasley and Granger…"

She told him everything she'd found out. "So," asked Marisa once she'd finished, "can you shed some light on what all that was about?"

"I know Dobby – he's the Malfoys' house elf, very weird. So, I'm guessing he doesn't know any more than I do. Polyjuice Potion makes you look like someone else, be on your guard around Potter, Weasley and Granger – you need a bit of a person, so don't let them get hold of your hair."

Marisa nodded.

"The Chamber was opened before fifty years ago – I've done a little research and the person who was arrested for it was…" He paused, for the sake of creating drama. "Hagrid."

"No way!" said Marisa. "He can't possibly be – I mean, everyone knows he loves monsters, but something like that – "

"I agree," replied Leo. "That makes it extremely likely that he was framed."

"And that's all the information we have."

"Yes."

"So, what do we do about the Polyjuice thing?"

"Nothing, as yet. I'll see if I can catch them and confront them somewhere where Draco won't see. If you happen to be passing that bathroom, have a listen in to find out how they're getting on. However, I do have a few things I think we could try without too much risk…"

Marisa smiled slightly. "Such as?"

"Geanology. Pure-blood wizards are big on their ancestry, so we should be able to find out who the possible descendants of Slytherin are. And there are charts in the library here – I think we should look now. You do your Potions essay; we don't want anyone getting suspicious."

She nodded and retrieved parchment and quill from her bag. Five minutes later Leo returned, carrying a heavy book entitled The Wizarding Descendants of Salazar Slytherin, 1000 AD – 1200 AD.

"This may be a bit tedious. Wish me luck." And he opened the book, while Marisa began writing out the properties of Flobberworm mucus.

Two hours later, they were still there. Marisa was running out of essays to write, having by now done Potions, Transfiguration and Herbology, and was working on a particularly dull History of Magic essay.

Leo, meanwhile, had pored over three massive geanology books and was now on The Wizarding Descendants of Arthur Gaunt, 1200 AD – 1400 AD.

"Any luck?" asked Marisa.

"Kind of," replied Leo. "It's really tedious – you never know when the line you're following is just going to stop and make ages of work be all for nothing. This one looks fairly promising, though, I think it might get somewhere."

"Can you remember the top ten causes of the Second Goblin Rebellion?"

"Yes, but I thought catching the heir of Slytherin would be more important than getting top grades from Professor Binns."

Marisa shot him a glare but had to acknowledge that he had a good point. She could remember six or seven of the reasons, so she'd be able to at least make a decent start without help.

"Hello."

It was Draco. Marisa spun round to glare at him and cover up Leo's hastily picking up a quill and beginning to write on a spare piece of parchment.

"Hello," she replied cautiously.

"What are you doing?"

"Writing essays," she said, trying not to sound too guilty.

"What's that big book, then?" asked Draco. He was pointing to The Wizarding Descendants of Arthur Gaunt.

"Oh," said Leo, looking up. "Hey, Draco. Just something I needed to look up for History of Magic."

That produced the desired results: Draco's eyes glazed over and he said "Oh, right."

"We're working on that at the moment," continued Leo, feeling a little mischievous. "Would you like to join us?"

"Yeah, do, Draco," said Marisa, catching on. "It's really fascinating – I find Professor Binns makes the subject so interesting – really makes you think about all those goblin rebellions – "

Draco looked at her as if she'd gone mad. "No, sorry – I have to go – uh – wash my hair." He made a speedy exit.

Leo and Marisa looked at each other for one long moment, and as soon as Draco was out of earshot, they simultaneously burst out laughing.

"Wash his hair?" Marisa choked out between giggles. "That is literally the worst excuse ever!"

"Did you see the look on his face?" Leo said, managing to compose himself a little but still grinning from ear to ear.

"Good way to get him off our backs," said Marisa, gulping in air. "Remind me to use that trick some time."

"Yeah," said Leo, and they returned to their tedious work, minds much refreshed by the laughter.