As the days passed at Hogwarts, tension simmered among the Slytherin students. Andrew and Rabastan plotted their malicious prank on Mary Macdonald with increasing fervor. They were fueled by their desire to impress the Dark Lord. Severus, Regulus, and Dan's reluctance to join in on the prank only seemed to further motivate them. One day, Andrew and Rabastan cornered Severus, Regulus, and Dan as they made their way to Potions class.

"Severus, Regulus, Dan," Andrew said, his voice dripping with annoyance. "Still trying to be swots, are we? You think you're better than the rest of us?"

Regulus stepped forward, his demeanor calm but firm. "We're not interested in your pranks, Andrew. We have other priorities."

Rabastan stepped closer, his eyes flashing with malice. "You're all making a big mistake. Do you really think that burying your heads in books will make anyone look up to you? It is not too late to join our prank. You can still join and try to impress Him."

Severus squared his shoulders, meeting Rabastan's gaze unwaveringly. "I don't care what the Dark Lord thinks. And you are making me late to potions class."

Dan, usually quiet and reserved, spoke up with surprising determination. "We're focusing on our studies. We want good grades to secure our future careers. Politics and pranks aren't our priorities."

Andrew and Rabastan exchanged a glance. They both realized their attempts to sway Severus, Regulus, and Dan had failed. With a final sneer, they turned and walked away, muttering to each other about their plans.

Later that evening, Severus, Regulus, and Dan met up in the dormitory.

"Not doing anything to stop it, feels just as bad as joining the prank. Since we know when and what their plan is to prank Mary," Severus admitted.

"You are right. We can't let them do this," Regulus said, his voice low but resolute. "We have to stop them."

Severus nodded, his mind racing with possibilities. "I have an idea," he said slowly. "It's risky, but it might just work."

Dan frowned, his brow furrowed in concern. "What do you mean, Severus?"

Severus explained his plan. They would use Polyjuice Potion to transform themselves into the Marauders. By impersonating them, they could face Andrew and Rabastan. With a bit of luck, their story could get Andrew and Rabastan expelled from Hogwarts. Most importantly, no Slytherin would know how they played a role in it. Meaning that there would be no revenge from Andrew or Rabastan towards them.

Regulus hesitated for a moment, weighing the risks and the potential consequences. "It's dangerous," he said finally. "But if it means protecting Mary, I'm in."

Dan nodded solemnly. "Count me in too. We can't let them get away with this."

With their decision made, Severus owled Lucius. Lucius soon owled them the polyjuice potion back. There was no time to brew it.