It was a completely ordinary day at Hogwarts. The headmaster was eating lemon drops, the amphibian defense teacher was handing out detentions to everyone who got a right answer, and the potions teacher was gleefully tormenting students while concocting his latest scheme to get Harry Potter expelled. In the library, a boy with a lightning bolt scar and a girl with bushy hair were researching methods to keep their secret defense club hidden. It was an ordinary day, that is, until the girl came across a reference to the Fidelius charm.

"The Fidelius charm is a complex, multifaceted and potent charm used to conceal a secret inside an individual's soul. The information is hidden inside the chosen person, or Secret Keeper, and is henceforth impossible to find – unless, of course, the Secret Keeper chooses to divulge it. When the charm is cast, any person who knows the secret - besides the caster and the Secret Keeper – instantly loses the knowledge. Of course, the caster cannot divulge the secret; should he or any other person with whom the Secret Keeper has shared the information try, their attempt will simply be overheard."

"Wait, Hermione – there is no limitation?"

"Not that I can find…"

"How do I cast it?"

"Point your wand at the person you desire to be secret keeper, say 'Mando tibi cum' followed by the wording of your secret. It is important that-"

Harry interrupted, pointing his wand at Hermione: "Mando tibi cum 'the incantation for the Killing Curse is Avada Kedavra'!"

"Harry what-"

"Mando tibi cum 'the incantation for the Cruciatus Curse is Crucio'. Mando tibi cum 'the incantation for the Imperius Curse is Imperio'."

"Honestly, Harry. If you could remove the knowledge of a curse like that, don't you think someone would have already done it?"

Harry looked around, spotting Terry Boot at an adjacent table. "Hey Terry, the incantation for the Imperius Curse is imperio. Mind telling me the incantation for the Imperius Curse?"

Harry and Hermione watched in disbelief as a blank look crossed the Ravenclaw's face. "I'm sorry Harry, I don't know it."

"…"

"…"

"Well Hermione, you must admit the book did say the charm was potent. And perhaps…"

"Harry, you've got that look in your eye."

"What look?"

"The I-have-a-stupid-crazy-idea-that-might-get-us-all-killed-look. You know. The one you usually get."

Harry put on his most innocent expression. "I honestly have no idea what you mean, Hermione."

The only response was a huff and a pair of crossed arms.

"Alright, so I do have a crazy idea. You know how the ministry is lying to everybody?"

"It's kind of hard to avoid spotting. What with them ignoring the return of You-Know-Who and everything."

"Well… Mando tibi cum 'the ministry is not lying about the return of Voldemort'."

Across the castle, students suddenly began screaming. In a sixth year defense class, Dolores Umbridge managed to look simultaneously horrified and triumphant before passing out, clutching her heart. In the Ministry of Magic, Amelia Bones dropped her monocle on a desk, while Cornelius Fudge had a face matching the color of his bowler. At a table in the Hogwarts library, Terry Boot shouted a horrified 'Oh my god You-Know-You is back'. Hermione merely stared with an open mouth.

"Uhm. Guess it worked?"

"Harry."

"So… I would cast it again to hide Dumbledore's Army, but it doesn't really seem necessary anymore…"

"Harry."

"I mean, we'll probably be allowed to train for defense now that everybody knows that Voldemort is back..."

"Harry."

"Perhaps we'll even get a proper defense teacher…"

"Harry James Potter, do you realize what you just did?!"

Snapping out of his reverie, Harry turned to his companion. Upon seeing the indignant expression on her face, the throbbing vein in her forehead, and the hands fisted at her sides, he responded with the only defense he could think of: "Uhm… Helped you get a better defense teacher for our OWL year?

"Honestly, Harry! You just brainwashed everybody! Better defense teacher… Hmph!"

"Well, you've got to admit it will be easier to wage war against… him… like… this…"

"Harry! You have that look again! Stop!"

"Mando tibi cum 'Lord Voldemort is not a half-blood named Tom Riddle'. There, that should lose him some followers."

Hermione's irate scream was completely drowned out by a shout from the other end of the library. "The Dark Lord is a half-blood? My father will hear about this!"

"Hmm. He's got a point. If we can do this, then so can the Death Eaters… Mando tibi cum 'the first part of the incantation for the Fidelius charm is mando tibi cum'"

"Honestly, Harry. That was completely unnecessary. You know the other side doesn't use logic. And while I can keep your attention from the shiny, world-breaking charm: Please stop messing with reality?"

"Oooooh, Shiny. I have a good one. Mando tibi cum 'Lord Voldemort has legs'."

In the town of Little Hangleton, a certain Dark Lord collapsed to the floor with a furious scream of 'Potter'. This was complimented nicely by the supersonic 'Harry!' that emanated from a certain female in the Hogwarts library.

After a few minutes of screaming, pulling her hair, and walking in circles, Hermione finally sat down with a defeated look. "Alright, if you can't beat them… Join them."

"That's the spirit! Got any good ideas in that brilliant mind of yours?"

Despite being somewhat placated by the compliment to her mental acuity, Hermione still had an annoyed tone in her voice when she responded. "Honestly, Harry. Of course I do."

Harry groaned as he recognized Hermione's lecture-imminent voice.

"Under common circumstances, human knowledge interacts with reality under an open world assumption; that is, if a piece of information is not known, then it is not necessarily because it is false. What the Fidelius Charm does is to enforce a mental closed world assumption on the piece of reality protected by the Charm; that is, the mind is made to believe that the unknown – the secret – is false."

"Hermione, I'm lost. Can you start over from 'common circumstances'? Or skip to the end?"

Hermione merely huffed and continued undaunted. "What your thoughtless experimentation proves is that by making the negation of a piece of information unknown and thereby false, you make the negation of the negation true – thereby planting the piece of information in the mind."

"Honestly, Hermione."

"So far, you have used it to plant a general statement. I am going to plant a conditional statement."

"I still don't follow."

"Honestly, Harry. Watch and learn. Mando tibi cum 'It is not true that if a person bears the Dark Mark or has been resurrected by a dark ritual then he must go to the ministry atrium, expose his right arm, and drink a vial of Draught of Living Death every twenty four hours in order to survive.'"

"…"

"You may compliment my brilliance now."

"…"

"Or applaud, I guess. Whichever you prefer."

"…"

"You could of course ask me to write down my findings and nominate me for the Magical Nobel. Or the peace prize, I guess, if it was not for the statue of secrecy. I did just end the war."

"…"

"Harry. You have the look again. Whatever you're thinking is not a good idea."

"…"

"Harry!"

"…

"Harry James Potter, you will not mess with reality again!"

"Mando tibi cum 'Harry James Potter and Hermione Jane Granger are not rulers of the world.'"

"Honestly, Harry!"