"Oh, Peter, this is going to be brilliant," Sirius said excitedly as he wrenched open one of the dungeon vents. All four of the Marauders crowded around it, peering down the air duct that they knew led into the Potions classroom. They were meant to be attending their final Potions class before the Christmas holidays, but instead they were availing themselves of the opportunity to pull off a prank they'd been planning for nearly a month. Even Remus was involved, having agreed to stand lookout—mostly, Peter suspected, because Potions was his least favorite class and he didn't want to endure it without any of his friends. Usually he tried to steer clear of this sort of thing.

"Hurry," Remus said nervously, peering down the darkened hall. "We don't have time to stand around all day."

"All right, Moony, we're hurrying," Sirius said with a hint of exasperation, though he ruffled Remus's hair affectionately at the same time. "Ready to change, Wormtail?"

Peter nodded, quickly shrinking himself down into his rat form. As always, everything seemed disorientingly big after he transformed, his friends' shoes now the size of his entire body; he shifted nervously every time one of them took a step, their feet pounding down like thunder against the stone dungeon floor. James lowered his hand and let Peter climb into his palm, lifting him up until he was again at eye level with the other Marauders. James and Sirius tied a Spoculus to his back (a small device resembling an eye that would allow them to see everything around Peter, given by Sirius as an early Christmas present to James), and each of them cast a Projecting Charm on him so he'd be able to hear their voices from far away. "Open wide," Sirius said—Peter obeyed, and Sirius placed a small Dungbomb between his teeth. Peter made sure not to bite down too hard lest he release its putrid scent too early.

"All right," said James. "You all set, Wormtail?" Peter did his best to nod around the Dungbomb. "Here we go, then."

James placed his arm into the open air duct, letting Peter climb off and scurry down it. Glancing behind him, he saw James and Sirius poking their heads inside and giving him encouraging grins. The grins only made Peter feel more nervous—he knew they would not be happy with him at all if he messed up their big plan.

He ran and ran and ran, the distance seeming excruciatingly long to his miniature rat self before he reached the vent cover leading into the Potions classroom. The Marauders had already loosened its screws in preparation for today, so it was easy for Peter to curl his rat toes around them and pop them out. Then, waiting for the commotion in the classroom to rise to a loud enough volume, he pried the vent cover off with his teeth and slid it carefully into the duct behind him before crawling out the hole and down to the ground.

"Excellent, Wormtail," James said into Peter's ear. "Now you've got to get to the back of the room without anyone spotting you."

Fortunately, the classroom was dark and shadowy enough for Peter to slip unnoticed past Slughorn's students by sticking close to the wall. Peter had no idea what potion they were brewing, but whatever it was smelled good, like peppermint and flowers. All the better for their Dungbomb prank.

"Ooh, there's Lily," Sirius said as Peter slunk by her. "You could always put the Dungbomb in her potion instead; I wouldn't mind."

"Absolutely bloody not, you git! Evans is off-limits."

"Right, right, I know."

Peter had reached Snape's workbench in the back corner of the dungeon, which he was sharing with his friend Mulciber. Snape was frowning over his ingredients, several dried herbs and salamander tails, and was scribbling something down in the textbook beside him. He appeared to be intently focused on the work in front of him, which was good for Peter.

Peter scurried up one of the legs of the table, waited for Snape to turn to instruct Mulciber—"The parsley works better if you crush it first, you don't want to put it all in at once"—and made a quick dash for Snape's cauldron, climbing up its side, crushing the Dungbomb between his teeth to release its stench, and dropping it into the potion before darting away.

"Yes, Wormtail!" James exclaimed as he returned to the ground and scuttled back across the floor. "Brilliant job! A masterful performance!"

"Wait there a minute, Petey, so we can see his reaction," Sirius said excitedly. Peter stopped by the wall and turned back towards Snape as the scent of the Dungbomb began to pervade his potion and send noxious fumes up from it—even with his poor rat's eyesight, Peter could see the confusion twisting Snape's face. Mulciber made a retching noise and slid his chair as far away from the potion as he could.

"I—I did everything right," Snape murmured. Anxiously he grabbed at his head. "I don't know what could've gone wrong…."

"Is that Snape's potion?" Peter heard Mary Macdonald ask. By this point, the rest of the class had all turned back to the Dungbombed cauldron, shocked that the class's best student could have made such a mess of his brew. Professor Slughorn was headed over to him, looking equally confused.

"I've brewed this potion before…. It's never looked like this, I—I don't know…." Snape's sallow cheeks had gone beet-red, and he looked like he wanted to melt into a puddle. James and Sirius were laughing hysterically into Peter's ears, so loud he couldn't hear what a disappointed Slughorn was murmuring to Snape.

He did, however, hear the startled shriek of Lily Evans as she leapt up onto her chair and pointed her finger at him. "A rat!" she cried.

Several of the other girls screamed as well, and even a couple of the boys. "Well, someone catch it!" Slughorn called to them. "We can't have pests contaminating our brewing space!"

"Bollocks, Peter. Run for it!"

"Oh, now your girlfriend's really done it, Prongs. Told you we should've Dungbombed hers instead."

"Shut it, Sirius. Peter, run!"

Peter sprinted across the room as fast as his tiny legs could carry him as Stupefys and Impedimentas rained down around him. He zigzagged to avoid the spells, one of them missing his head by less than in inch, and kept his eyes trained on the open vent ahead of him while his heart beat fast enough to explode in his chest. Finally he reached the vent, leaping into it and not pausing to catch his breath until he'd made it all the way back to the other end and the safety of his friends.

Sirius helped him out and placed him on the ground so he could transform back; as soon as he had, the other Marauders crushed him into a massive four-person hug (even Remus, pale with concern, deigned to join in). "Thank Merlin you made it out of there," James said as he linked his arm around Peter's shoulders. "We were scared Slughorn would chop you up for potion ingredients."

"Of course he made it out of there." Sirius beamed at him. "He's our Wormtail, isn't he? Fifth years casting Stunning Spells are no match for him."

Peter felt warm with pleasure at their words. He wasn't usually at the center of any of the Marauders' plans, but his Animagus form allowed him, for the first time in his life, to do things that the others couldn't. And now he was the one getting all the attention, all the praise from three of Hogwarts' best students. He wasn't just someone tagging along and laughing at their antics—they appreciated him for something he'd done on his own. Sure, the whole plan had been James and Sirius's idea, but he'd been the one to carry it out, hadn't he? And he'd been brilliant, James had said. Masterful.

For one brief, happy moment, Peter felt like he truly deserved to be one of the Marauders.