Severus Snape had always found the four idiots, i.e. the notorious Marauders very, very suspicious.

'I can't wait for the night, Moony. It's going to be so much fun,' said Black fondly, his hand patting Lupin like he was patting a puppy.

Ew. Night only meant one thing for Black: sex. Only someone as obnoxious as Black would share every detail of his dirty nights (which girl got her dream fulfilled? Snape wondered) with his friends, and only someone as obnoxious as Potter and Pettigrew would listen attentively with a big stupid grin like Black was the greatest comedian out there.

Not that Lupin wasn't batty.

'Be quiet, Padfoot,' whispered Lupin, 'bedroom talk. '

Oh God. Snape couldn't even imagine the quiet Lupin participating in dissecting Black's sex life in their dorm.

Snape was packing his trunk when he realized he had left his potions textbook in the dungeon.

'Gotta go pick it up now,' he looked at the clock, which pointed at eight at night. In preparation for O.W.L.s, it was not uncommon that students requested extra lessons and Slughorn gladly lent his dungeon in reward for their diligence. If Snape was lucky, he could even run into Lily there…

'I see we have the whole dungeon to ourselves,' a voice rang in the dungeon. Snape stopped just outside the door. Some bark-like quality of that voice made him uneasy.

Just as Snape decided he had enough patience for the muffled reply ( he would NOT admit that his annoyance was largely due to his failure in eavesdropping) and wanted to push the door open, the voices came again.

'Hmmm… Moony….'

'Padfoot, could we… uh… go back to our dorm?'

'Moooooooonyyyyy…. Mmmmmmm.'

Moony and Padfoot. Stupid nicknames. So it was Lupin and Black inside alright. Suddenly Snape decided he would rather retreat to the safety of the Slytherin Common Room now.

'My Moooooooony is my suuuuun, my sun is my Moooo– arghhhhhhhisdhfi! Were you lurking here, Snivellus?' Unfortunately, the very second Snape decided to return was the second the door burst open, revealing a messy-looking Sirius Black and a red-faced Remus Lupin.

Snape swore inwardly. While his whole life flashed before his eyes, he did not miss the fishy red marks on Lupin's neck, nor did he miss how the two sprang apart from a hug the second they saw him.

Snape picked at his pancake. Half of his brain was mooning over a certain redhead, half of it was stuffed with his self-invented spells and potions.

'… that was a good shag,' the annoying bark-like voice of Black rang again. 'He means… the shack,' panted Lupin, who caught Snape's sideway glance at him. Lupin's face flushed just a little bit, which resembled Lily's red hair.

'A good shag in a good shack, you mean,' Black laughed. Lupin shifted uncomfortably.

'What's the thing with the shagging shack? You've been talking 'bout that a lot lately. Another bird, Pads? ' sneered Potter. He tossed a peanut into his mouth but failed. 'By the way, where were you two yesterday? I was hoping we could raid the kitchen.'

'You can do whatever you like, Padfoot, but don't let me see anything during our monthly gatherings,' Pettigrew grinned.

The shack? The only shack Snape knew was the Shrieking Shack. So, the infamous Marauders were up to something in the Shack at least monthly, though Black seemed to use it more than often.

Snape was curious.

That's it. The Shack was the Marauder's secret meeting place. The Shack held all the answers to Snape's suspicions. And he was determined to find them all.

Snape had seen the Marauders sneaking out of the Common Room after curfew every now and then, but had always missed them once they got out of the castle. Tonight was an exception; with the new moon Snape could barely make out the two distinct shadows on the Hogwarts ground which were moving towards the Shack.

'You sure you have the map with us?' asked a timid voice.

'Quite. Can't have him walking in on us when we…' another voice answered, though the last few words were so quietly spoken that they were inaudible.

Snape watched as the shadows moved forward. The taller figure had its arm around the other's waist, while the smaller figure leaned closed towards its companion. They seemed to be having a stroll (when it's nearly curfew) and Snape had to tiptoe slowly behind them, which was very painful especially when his curiosity could not be satisfied by their pointless, silly conversation.

Black and Lupin again, thought Snape distastefully. However, he could not suppress his angry gasp when he found himself staring at nothing but shadows and trees. Black and Lupin had disappeared. Bugger!

From the day onwards, Snape became even more determined to find out what the Marauders, in particular, Black and Lupin, were up to. This, was the beginning of The Prank, aka the Snape-knew-about-Remus's-lycanthropy incident.