It was that Friday, in Potions, that Marisa got a chance to enact revenge on Draco. The Potions professor, Severus Snape, who was also the Head of Slytherin, was rather mean to Harry Potter and took a point from Gryffindor. If Marisa hadn't wanted Slytherin to win the House Cup she might have complained.

They were told to get into pairs to brew a simple potion to cure boils. Marisa had wanted to go with Leo, but he ended up with the other Slytherin boy – wasn't his name Theo? Instead, she was paired with Daphne Greengrass, who didn't utter any objection to working with a Muggle-born.

Once the potions had reached a reasonable stage, Marisa reached into her pocket and pulled out a Dr. Filibuster's Wet-Start, No-Heat Firework, kindly donated by Leo, while Daphne was stewing horned slugs.

As Snape was telling everyone to look at how well Draco had done the same, Marisa threw the firework. It landed in Draco's cauldron and there were two loud explosions.

"Potter!" called Snape immediately. "Thought you could use the explosion to prank Draco, did you? Well, you thought wrong. Fifty points from Gryffindor and a detention for you."

"But Professor – " stammered Harry Potter, "I didn't – "

"And a further five for lying. Another word, and I'll make it a hundred."

Marisa glanced around to see the effect of the explosions. Many people were covered in boils, but the worst affected was Draco, whose entire face was covered in boils. Along with many others, he walked up to the desk to receive an antidote from Snape.

Marisa felt rather uncomfortable. It was one thing to take revenge, and very satisfying too, but she didn't like an innocent person being blamed for it. Plus, the whole point of her plan was that Draco knew it was her fault.

She raised her hand.

"Yes, Miss… err…"

"Marisa King, Professor," she said in a rush, worried that if she stopped, she wouldn't be able to start again. "It wasn't Harry Potter who threw that firework. It was me."

"I see," said Snape icily. "Detention. And stay behind after class, I'd like to have a word with you."

Marisa nodded and began to focus utterly on her potion. A lot of the Slytherins were glaring at her, but she seemed to have made friends of the Gryffindors. She also noticed that Potter's detention and house points had not been revoked.

When the bell rang, everyone else filed out, leaving only Marisa and Snape in the room.

"It was not very wise of you to provoke Draco Malfoy. His family is extremely influential."

"It was not very wise of Draco Malfoy to provoke me."

"What did he do?"

"He called me a Mudblood."

For a moment, Marisa could have sworn Snape flinched. It was very odd.

"Very well. But it must not happen again. You may go."

Marisa left, very relieved.