Disclaimer: I'm not quite sure what the point of these disclaimers is. Either it is a copyright violation or not, and fanfiction is. That being said, as far as I know JK Rowling has not objected to fanfiction that did not try to pretend it was official and that was not sold for money. Both apply here, so I hope this is okay.
Real author's note: There is nothing more inspiring than bad fanfiction. In this case, the idea sprang from one that explained in great detail how much food one would need for a training session, where it came from and so on (sorry, can't recall the title right now) and then went on to explain other boring stuff in great detail. I thought one could write a good story about the inner workings of Hogwarts, though. Not sure if this is it, but if it isn't, I hope it will at least inspire someone to write better things instead.
As every transfiguration student knew, you couldn't just let food appear out of thin air. That was the problem. Oh, sure, wizards could make it appear as if they did so (nobody enjoys a good light show more than a powerful wizard), but magic would sooner or later demand it back. This was known as the Ulfrickson's principle, after Sir Ulfrickson, who woke up in January 1213 with most of his intestines missing after a particularly large meal.
The easiest way to repay the magic was to prepare an equivalent meal somewhere, together with some incantations so easy that even house elves could make them. This was the default method in all large wizarding kitchens, if alone to save on meal transportation. And there was no larger wizarding kitchen than the one in Hogwarts.
Dobby inspected the lettuce list for this week. Resource management in a kitchen this large was not an easy task. Apart from several hundred students and many teachers, the kitchen also prepared all food for the house elves, for the mere people (the food deliveries were part of the contract that allowed the founders to build Hogwarts in the first place), fourth and fifth helpings for Hagrid and his pets and so on. Being in charge of the kitchen was the greatest honor a house elf could hope to achieve, a position on par with a teacher. And as supreme master and vice roy of purchasing, Dobby was well on his way to reach that spot. No sir, Dobby was not squandering the gift of clothes that Master Harry had given him.
The lettuce list was uneventful, so he signed it off and turned to the meat manifest. Item after item was uneventful… no, wait, that one wasn't. He checked again, and the result made his eyes pop out (strictly forbidden in front of wizards. The sight of house elf eyes popping out even more is so frightening that several are said to have died from it). What to do? He couldn't tell his boss, or he'd loose his job immediately. He certainly couldn't expect help from the house elves he managed. Friendly as they were, none of them would mind if his job was open again. There was really only one person who could help him right now. With a loud crack, he disapparated.
Harry did not sleep well. There were the lingering feelings of guilt over the death of Sirius, the general uncertainty about the prophecy, but most of all, there was a house elf who had just apparated into his dorm room. Harry had long ago decided to stop considering this, or in fact anything, unusual, but there could still be no doubt that it was not helpful for getting a good night's sleep.
"Dobby… hi… sorry, still sleepy… what is it?"
"Master Harry must come with Dobby! There is great danger for Hogwarts and Master Harry's friends! Quickly!"
"Isn't there always… let me just get my…"
"No time! Master Harry must come right now!"
Harry listened. There was no sound of explosions anywhere, and the rest of the dorm room seemed to be sleeping. Still, evil had come at all times of day before, so he nodded to Dobby and started to get out of bed. The house elf was quicker, however. He grabbed Harry's arm and after a quick pop, Harry found himself in an undercellar that probably belonged to the kitchen, in a corner that seemed to have been transformed into some sort of office. He wanted to ask Dobby, but the elf was already gone again. After two more cracks, Ron and Hermione, both just as groggy as Harry himself, appeared as well.
"Mornn' Hry… wassup?" Ron groaned. Hermione wasn't more enthusiastic either.
"Wanted to sleep…"
"No sleep! Important problem!" Dobby had reappeared, talking in what was probably a normal voice, but seemed incredibly loud right now. He was, however, carrying a small tray with three cups of coffee, which helped brighten the mood a little. After a few sips, they all approached consciousness.
"Okay, so where exactly are we?" Ron asked.
"Looks like part of the kitchen storage rooms, but Hogwarts: A History is surprisingly vague about this part of the castle. I wonder why." Hermione was clearly upset that they had managed to find the one part of the school that her favorite book did not cover in detail.
"Is because wizards not be allowed down here. Kitchen is house elves realm. We sometimes invite friends such as you Masters, but Filch has to talk through door." Dobby seemed mighty proud of his kitchen. Then he furrowed his brow. "You masters better not enter without Dobby. That would not be good."
"Wait, are you saying house elves would attack us?"
"House elves like work. House elves not like interruption. Hogwarts house elves special. Last time wizard tried to enter by force, whole school in riot. 1768."
Hermione had found her footing again. "1768? But that was the year of the war about the new Bremham-Stolder curriculum, wasn't it?"
"Aye, Mistress Hermione, fight turned to that. Fighting started when bad wizard wanted inspect kitchen cleanliness. This kitchen be always clean. No inspections."
"Right, yeah… but why did you wake us up?" Ron was still sleepy.
"Masters have to see this."
Dobby spread out a huge pile of parchment on the desk. Harry could glimpse some of the titles, including pear protocols, beverage bills and tomato tables, each for specific time periods, but Dobby quickly brought up the most recent meat manifest.
"Look there, Master Harry! Salted orkik sides, twenty-three of them! Dobby no order no such thing, but it here on order form" - he pulled out another piece of parchment - "and that no Dobby's writing!"
Harry was confused "Okay, so someone ordered salty something without permission. How bad is that? I mean, can't you just find who did that? Send it back?"
"It's not that simple, Harry. Orkik sides look like chicken, taste like chicken, and ten to fifteen minutes after you ate them, you're dead", Hermione explained. "That amount would be enough to kill… 80 students at least. That would be bad indeed."
"Unless it's for Slytherin" Ron interjected, which earned him an icy glare from Hermione.
"Okay… so what do we do?" Harry asked Dobby. "If I read this deposit diagram right, you already dumped it all as 'doese nots meet quality requirements'. Maybe that was just some error?"
"No, Master Harry, this ise worse. Not even a great wizard such as Harry Potter can just buy orkik meat. This came smuggled in."
"Bloody good smuggler that is, leaving his smuggled goods on the list." Ron remarked.
"Don't be stupid, Ron. These lists are clearly magical and register anything that goes in. And I guess without the faked order, some spell would have sounded an alarm at the delivery." Hermione glanced at Dobby to confirm her theory and was relieved to see that he nodded.
"Dobby is supposed to store order form so that nobody can add to it. Someone added to it. That evil wizard nearly killed hundreds, and it is Dobby's fault! Bad Dobby!" Harry had to quickly restrain the elf as he tried to beat himself to death with a ruler that was placed on his desk. After several reminders that it was Dobby who had saved all their lives, he finally calmed down.
"Masters must see that this is horrible! The dark wizard or someone tried to poison us. Tomorrow he will see that masters are still alive. He will know Dobby stopped him, and he will try again. Masters must find him and kill him or else we all die!"
After a momentary pause, Ron spoke.
"Okay, so… no pressure. So how do we start?"
Dobby looked up.
"Perhaps it be best if Dobby give Masters a tour."