The year 1977...
James Potter checked the Map for any obstacles on the way towards his objective, and relaxed when he saw the path was clear. He tapped the Map, and murmured "Mischief managed." A month ago, he had finally succeeded in getting Lily Evans to go out with him, and since then, had been indecently overjoyed.
It was one A.M, and the Common Room was deserted, partly because of the time, and partly because James had threatened to hex the three remaining boys, who were ribbing him about his plans with Lily, if they didn't clear out. James smiled at the three dots, now ensconced safely in their dorm, and was doubly glad he had the Map. Now they couldn't track him either.
He turned to see Lily Evans descending the staircase from her room and grinned at her, desperately happy to see her. She was smiling back at him, which was a pleasant yet strange change, considering that she had spent the past six years ignoring, insulting, or avoiding him. But then, the path of true love never did run smooth.
"Ready for our night-time stroll, Evans?" Her red hair was pulled into a ponytail and her green eyes danced. "I still say this is a terrible idea, Potter. But then again, so was the whole of last month." She winked at him and laughing, he took her hand, reveling in the feeling when she squeezed back. They exited the portrait hole, careful not to wake the Fat Lady and pulling the Invisibility Cloak over them, proceeded to walk towards the grounds.
A good while later, James and Lily started back towards the castle, only to stop as a huge black dog joyfully gamboled towards them, frantically wagging its tail. Even as Lily bent down to pet it, James crossed his arms and glared at it. So much for privacy.
"James, why is it that every single time you see this adorable creature, you start scowling like he did something unmentionable to you?" If only she knew, James thought to himself and sighed, before he too started to stroke its thick fur, and the dog happily barked.
The three of them made their way through the castle, and all was going well until the dog accidentally knocked over a suit of armor. Almost instantly, Filch was there, and James barely had time to throw the Cloak over himself, Lily and the dog, who had morphed back into his human form of Sirius Black. What he didn't notice was the Map that had fallen from his pocket when he had pulled the cloak out.
Lily almost screamed in shock at the dog's sudden transformation, but Sirius managed to clamp a hand over her mouth in time. The three moved as quietly as they could back towards Gryffindor Tower, and none of them saw Filch frowning, and picking up the blank parchment.
In the safety of the Tower, Sirius started laughing at Lily's expression of astonishment. James stepped in. "I can explain, I promise." She paced back and forth, before pointing at Sirius and groaning. "So all those times in Hogsmeade and-" James turned slightly red, and nodded. Sirius was snickering- "Oh, don't worry. I turned away when you two were snogging. Even I have some things I can't watch." It was Lily's turn to blush, and she buried her face in her hands. Her voice, slightly muffled, said, "No wonder you looked at the dog like you were going to kill it. I want to strangle him myself now."
Sirius spoke up again- "You do realize James can turn into an animal as well right? He's a stag." Lily gaped at him in amazement before she muttered, "So that explains your Patronus." And mine as well, she thought to herself.
James was glaring at Sirius again. "So how did you find us?" Sirius looked very pleased with himself. "Well, dogs do have an exceptionally good sense of smell, and you stink, Prongs. Did you think taking the Map away would prevent a truly dedicated person from locating you? Now hand it over."
James reached into his pocket and blanched. He patted his clothes and checked his pockets again. "I can't find it. I must have dropped it in the corridor, when I pulled out the Cloak!" It was Sirius' turn to glower. "Bloody brilliant work Potter! You've lost our most valuable tool to Filch, of all the people possible. And after the last time we broke into his office, he's made it impossible for anyone to do it again! Wait till Moony and Wormtail hear-"
Lily interrupted them. "What did James lose?" Sirius threw him a dirty look before replying, "I could answer his heart, to you, but then that was years ago." She rolled her eyes. Sirius went on, throwing an arm around her shoulders. "Listen well Evans, and let me tell you the story of the greatest invention made by the four most brilliant students this school has seen- well, three of us are at any rate..."
Meanwhile...
Filch sat in his office, casting suspicion-laden looks at the parchment he had found. It looked awfully similar to the ones he had often seen in the hands of those four Gryffindor troublemakers. Tapping it with a finger, he muttered, "I'll ferret out your secrets yet, my beauty. I, Argus Filch, haven't been the care-taker of this school for all these years without a reason." He almost jumped out of his chair when he saw lettering appearing on the Map, and gingerly pulled it towards him to read it.
Mr. Moony bids hello to Mister Filch, and deeply regrets to inform him that he is a mean git with a face that looks like a pile of owl droppings.
Mr. Wormtail agrees with Mr. Moony, and asks Mister Filch to take a bath before doing anything else as the stink is unbearable.
Mr. Padfoot registers his amusement at the fact that Mister Filch seems inordinately proud of his post considering he is nothing more than a reviled self-glorified cleaner.
Mr. Prongs asks that Mister Filch more carefully hides the fact he can't use magic properly, and refrain from tormenting students in the future.
Filch immediately grabbed the Map and stuffed it in a drawer marked Classified and Highly Dangerous, before locking it and collapsing back in his chair, wiping the sweat off his face and gulping down air, trying to relax. That thing was nothing but trouble. Better to lock it away safely here, where no one can get their hands on it...
Or so he thought.