BETA READ by Spin84
This is based on a cartoon I saw on Facebook.
The four Seventh Year Gryffindors lay lazily upon the high wooden seats of the Quidditch stadium, letting the sun hit them with its rays as they enjoyed their Saturday afternoon, in peace where no one else would come. At this time of year, most of the pupils rarely ventured far from the Great Lake, while a few of them remained inside, working on their last few essays of term. The four Gryffindor Animagi, however, couldn't be bothered. A Snitch long stolen was tossed between the Potter and Black boys. James lay one seat lower, gently throwing the tiny golden ball over to his best pal, who always returned it. It wasn't a game; it was more a way of keeping themselves occupied. Nonetheless, Peter Pettigrew, sat upright against the top rail beside Sirius' sprawled figure, eyed it much like a regular Muggle would tennis or football. Remus meanwhile, lay beside James with his hands tucked behind his head carelessly.
"Whose cat is that? I've seen it before a couple of times, but I can't recall where," Remus wondered when he opened one eye blearily, and saw a stray grey tabby prowling below them on the field.
Sirius caught the Snitch securely in his left palm and leant up on his elbows to look at what Moony had seen. A smile came across his youthful features, his eyes glinting wickedly at what he saw.
"Padfoot, no," Remus said, "it is the middle of the day. If you get caught, we're all going to be in huge trouble. Unregistered Animagi–"
"Oh hush," Sirius said. "I'm going to have a little bit of fun, that's all." With that, he raised himself off the seat, morphing into a large, black dog as he sprung across the benches.
"Padfoot!" James, too, yelled after his pal, seeing the risk ahead. If they got caught, they might even need to hand in their wands at the Ministry; Remus had been quite right. To his own horror, he watched Sirius race down to the pitch at a terrific pace. He swore that he could see the panic in the cat's eyes as it saw the dog and began to run, Sirius lolloping after it, chasing it from their view into the Forbidden Forest.
James moved, intending to go after them, but Remus held him back at once. "The cat will climb up in a tree where Sirius can't reach it, and he'll return here, bored in a few minutes, I'm sure," he reasoned. James, who had to admit that Moony had a point there, laid back down on the seat once more, just shaking his head. Oh, Padfoot…
However, unlike Remus and James had thought, Sirius Black was faster in his Animagus form than the poor, frightened cat. He never quite intended to hurt it, of course, but it never even had the chance to climb a tree, before he threw himself atop of her, keeping her from escape.
Sirius watched in horror as the cat that he had been chasing and just pinned to the grass turned into no other than Professor Minerva McGonagall – who looked far from happy as he himself morphed into her Seventh Year and more-bothersome-than-ever pupil. He visibly swallowed at the fury in her teal green eyes, gazing up from beneath him.
"You've just earned yourself detention, for the rest of the year."
Sirius eyed her, shock giving way to his familiar crooked smile. "What if I were to kiss you?" he wondered, realizing he was still dominantly straddled over her, although now in human form.
"Sirius Black! You had better stop this nonsense at once, and would you be so kind as to get off of me… unless you would like me to hex you into next week!"
He did as she said, eyeing her with a look of fake innocence he knew had never worked on the professor anyway. He had to try, at least. He watched as the elder witch first sat, then stood and rose to her full height. She was slightly taller than him, even if only by a couple of inches. "Professor…" he began.
"I won't hear it, Mr. Black!" she said. "I'll never be more relieved than this year to see certain pupils leave. You and Mr. Potter have caused me more grey hairs than any other of my pupils put together in all my years as a teacher! Now, you're of age, and will be leaving Hogwarts in less than a month. Therefore, I do expect you do the right thing, concerning your being an Animagus, and make this ability known to Ministry officials yourself once you have left, to have yourself registered, at least."
"I…" Sirius began again.
McGonagall sighed, gently pinching the bridge of her nose to keep the impending headache at bay. "You will be at my office at six tonight," she said. "No excuses, no being late, or you will be in much more considerable trouble than you already are, I assure you."
"Yes, Professor McGonagall."