Insane Asylum escapees!

Mr Rock, the dementor killing rock

The train skidded to a stop and the air got colder.

"What - is it winter already?" Harry asked, sleepily, waking up from his nap. Blaise, the only other one in the compartment besides the sleeping professor, glared at him.

"Potter, I take back every nice thing I've ever called you," Blaise told him, "and replace them all with 'You're an idiot'. Dementors are close by, probably searching the train for Sirius Black."

"Don't see why. He's obviously not here," Harry said, pulling out Mr. Rock (the rock he took from the chamber the year before; he called it Mr. Rock to freak out the Dursleys and the name stuck) and tossing it up and down, "Unless he disguised himself as Mr. Rock." Harry stared suspiciously at his rock for a moment before shrugging and continuing to toss it up and down. Blaise rolled his eyes.

"If you don't believe in magic, how can you possibly believe that Black is pretending to be your rock?" Blaise asked, eying Lupin. He could have sworn he saw Lupin twitch.

"You'd be surprised at the amount of technology the government keeps from us. Black might have gotten his hands on a super hologram creation device or something like that," Harry replied.

"First your and 'Insane Asylum Minder in Training', and now you're a conspiracy theorist." There! Lupin twitched! "What's next Harry?"

"I'm going to be an astronaut." And Lupin twitched again. There's no way he was really sleeping.

"What the hell?" Blaise cursed, as the door to the compartment opened.

"Holy shit! It's Black (guess who twitched again) dressed up as a Nazgûl! Mr. Rock, sacrifice yourself to protect us!" Harry closed his eyes and threw the rock as hard as he could. He heard a smack and a thump before he risked opening his eyes.

"Harry," Blaise said calmly, "Congratulations. You just knocked out a Dementor, using nothing more than your pet rock."

"…"

"…"

"Is that a good thing?" Lupin shuddered and Blaise was damn sure he was awake.