AN: For the 'Dog' challenge at fan-flashworks. Also for the 'transformations' square of my trope-bingo card.

A shiver ran through the rat in the center of the Gryffindor room - and then it shot up rapidly into Peter's chubby figure. He grinned at his friends, who had been clustered anxiously around him.

"It worked! I can do it!"

James high-fived him, Sirius let out a war whoop, and Remus gave a heartfelt sigh of relief. If anything had gone wrong, when they were only doing this because of him… But nothing had gone wrong. With Peter's success, the three new Animagi had all gone through their first transformation into animals and back safely.

"'What if you end up canaries? What if you end up goldfish?'" Sirius quoted mockingly, with a laughing look at Remus. "Told it you would be fine, didn't I?"

Remus rolled his eyes. "I almost wish you had turned out a goldfish, if that's how you're going to be. It's not as if you were much brighter than one!" But his tone was affectionate, and he grinned back.

"Never mind goldfish, this is brilliant!" James said. "We're exactly what we need."

"You and Sirius, maybe, you'll be big enough to… well, to be useful," Peter said, his face turning glum as he dropped down onto a window seat. "I don't see how much good a rat's going to be."

"You're joking, right?" James asked, incredulous. "It's the most useful of all! It's you who's going to get us into the passage under the Whomping Willow, for a start. You'll be the only one able to get past the branches."

"Oh, that's true," Peter said, looking more cheerful.

James continued, warming to his theme. "You can go anywhere in Hogwarts - or anywhere, really - without anyone noticing you as long as you're careful. Sirius and I are going to be pretty much confined to the grounds."

"Speak for yourself," Sirius retorted. "A deer can't very well run around the hallways, but I bet we could pass a dog off as someone's pet."

"No we couldn't," Remus said. "It's an owl, a cat, or a toad, remember? Anyway - "

He was cut off by Peter sitting bolt upright with a squeal. "Cats! Mrs Norris! She'll eat me if I go wandering around Hogwarts as a rat!"

"Not if you're careful, or if we're distracting her somewhere else," James replied, expression thoughtful as possibilities for pranking unfolded themselves before him.

"Oh, please, let's pass me off as someone's pet so I can chase Mrs Norris around the castle!" Sirius exclaimed, with vivid recollection of the many times the cat had brought Flich - and doom - down upon their heads.

"Anyway," Remus repeated with emphasis, "you promised to be careful not to let anyone get suspicious, and to stay out of notice. A 'pet dog' that appears out of nowhere halfway through the term and deliberately targets Mrs Norris is going to be noticed!" Even if, as he admitted to himself, it was a very tempting idea, the risk was too great.

Sirius looked ready to argue, but James nodded, looking solemn. "Remus is right, we shouldn't risk it." He kept a straight face for a moment, then chuckled at his friends' surprised expressions. "There's no point getting caught just for Mrs Norris, we can do much bigger stuff than that."

Sirius laughed and nodded, Peter demanded to know what James was planning, and Remus flopped back onto his bed.

"Idiots," he informed the ceiling mournfully. "I am surrounded by idiots."

Sirius looked at him, eyebrows raised. "So you won't be joining in on this?"

"Of course I am, someone has to make sure we all make it through in one piece," Remus said in his most martyred tone - not that it fooled his friends; and if it had, the sparkle in his eyes, the alacrity with which he sat up and joined in the planning, would have given him away.