A/N: Hello ladies and gentlemen. Welcome to a new rabbit hole.

I don't know about all of you, but I simply love Halloween. It's the perfect holiday. And you know what, in honor of this amazing holiday, I'm going to finally play with an idea that's been knocking around in my brain.

It was brought to my attention a little while after The Dark Knight Rises came out. Did anyone see the Joker in Blackgate Prison? Noooo...? Then where on Earth could that mad man be? Well... the only place they could put him would be Arkham Asylum. But, everyone else was moved to Blackgate. So wouldn't that mean that the Joker is going to be the only person in Arkham Asylum? Well then... if that's the case, what happened to him while Bane was taking over Gotham and madness once again overtook the city?

Shall we explore this possibility? Surely you're as curious as I am.

This chapter is just a little experiment to get a feel of things and give a bit of background.

Arkham's One Horror

Chapter 1

A few years ago, Gotham City had no hope. Gotham City was a cesspool of evil, corruption, and fear. Everyone put their worst foot forward, on top of the heads of everyone else. If you weren't in that inner circle, you were a mere puppet. A tool. A bug.

But then, everything changed. Someone stood up to the norm. Someone disobeyed the rules the mob bosses spent years setting up. He shook them down to their core, tore down their walls, and did his best to destroy anything they built. He was the nightmare of every shadow Gotham had bred.

The Batman.

A Dark Knight to chase all the other little shadows away.

He scared them. And he had to. The only way to control fear is to put fear into it, by putting hope into fear's victims. It's an endless cycle. A cycle the new victims were desperate to beat.

So they placed a new shadow over Gotham, something that would swallow up Gotham and its Dark Knight. Something that would spread like a virus, and infect everything it touched. Something that could put fear into the nightmare of Gotham's original shadows.

The Joker.

A man who could smile in front of the Dark Knight's stare.

No… no not a man.

A monster who would laugh at the city and all of its former shadows.

A creature that would drown Gotham in an everlasting night, smothering every bit of light it could cast.

And he succeeded, at least for a moment. He placed a bloody smile in the hearts and minds of all the pitiful Gothamites. He made them all cower beneath his dome of shadows while he looked over them and laughed at their horrified faces when they finally realized they couldn't use the light to hide from their true nature.

He helped them all discover that the monster didn't have to come from the outside.

The shadows didn't always come from a lack of light from the outside.

There's that little part inside of people… the part they always try to hide with their rules and their fake morality… the blackest part of them that could never be matched by the darkness outside.

It was always there. The Joker just helped them find it.

But then the Dark Knight cheated. He smoldered the spreading darkness. And when the light returned to Gotham, the people of Gotham pretended that they never saw it. They pretended it still didn't exist.

And after seeing the hidden darkness within themselves, the people of Gotham were determined to never see that darkness again. They wanted to obliviate the memory. They wanted to make sure there were no reminders of the life they led, or the reflection they had seen in the clear mirror when their falsehoods were taken away.

So they chased away every touch of darkness they could. And hid it all away. They put it in jails. Chased the helpless out of the city. Built up the hope of those who could grow.

And as for the new darkness? The thing that had… granted them a new lease on life? The one that had shown them the truth?

Of course, they had to put him away. Somewhere where they would never have to see him again.

Where had they trapped the shadow that ate all other shadows?

Well, in the best kept secret of Gotham of course.

Arkham Asylum. The last real back alley of Gotham these days. The last place that no one wanted to touch.

The Harvey Dent act had made it impossible for everyone else to plead insanity and be placed in Arkham Asylum. The mob thugs had been placed in Blackgate. The actual crazies had been placed in a real mental asylum.

No one had argued against the Joker's insanity plea. No one had tried to argue against his crimes against the city. No one had fought the Joker's transportation to Arkham Asylum.

They just wanted him gone. They just left him there to stew in his own shadows.

For the past eight years, Gotham had done its best to forget about the beast they had buried under stone and metal, guarded by a small force of twenty.

But how are stone and twenty mere men supposed to guard true darkness… when Gotham's days come to an end?