Okay, so...I may have another Batman: Arkham idea. Hopefully, this one will work out.

Now, this one came about after starting to play Batman: Arkham Knight. That particular installment of the series, I feel ambivalent about. Most parts are enjoyable, but the Batmobile elements (or at least those requiring Pursuit Mode: Battle Mode is FUN!) can go die in a hole, and the story has some elements I dislike (particularly Batman treating his allies, particularly Tim Drake, with utter coldness). But the concept of the Joker's blood being infectious appealed to me, and I decided to go with it. True, this story is set roughly halfway between Arkham Origins and Arkham Asylum, so Titan isn't a factor, but still...I think I hit upon a perfectly plausible way for Harry to become one of the Joker Infected.

Something that is raised in Arkham Knight is that each of the Joker Infected represents a different aspect of the Joker's personality and traits. I'll leave it up in the air what part of the Joker Harry will embody, but keep this in mind: at worst, Harry will be an Anti-Villain Joker. Arkham Knight (the character, not the game) is worse than what I intend for Harry to become. Oh, and this will be a Harry/Ivy/Harley pairing. Yes, I know Ginny is brought up as Harry's girlfriend/fiancee later on in the chapter, but I have plans for her...

ONE BAD DAY

CHAPTER 1:

ONE BAD IDEA

I stare at the form convulsing on the floor, mouth wide in a rictus smile as they die, laughing. I can't help but laugh myself. It's not a mirthful sound. It's like that coming from my victim, a tortured, painful thing.

I laugh as I die. Not in the same way my victim is dying. No, my soul dies as I laugh, as if each braying note carries a piece of my soul with it.

He was right, damn him. One bad day. Sometimes, that's all it takes to push people beyond the threshold of sanity and morality. I laugh because I get the joke, even if it isn't funny. I laugh because the alternative is to cry, to mourn my victim's passing, and my own.

This is the story of how Harry Potter died. And how a monster took his place…

"This is a really, really bad idea."

I said this while eyeing the vial filled with liquid that seemed to shift between colours, from purple to green, each colour too vivid to be healthy. It seemed almost alive, and malevolent. It was not hard to believe that part of it had come from one of the most notorious criminals to ever live.

The bushy-haired witch watching me nodded morosely. "I know it is. If it were up to me, we wouldn't be doing this as an undercover operation. We'd have you take the Invisibility Cloak and infiltrate wherever he's based in Gotham. But, well, the head of the DMLE has spoken. He wants this to be the field test of the improved Polyjuice formula."

I couldn't help but swear profusely. I really, really did not want to disguise myself as this disgusting monster. A monster who, even now, was kept in a comatose state courtesy of the Draught of Living Death, lying on a nearby bed. Even in sleep, that damned grin twisted his features, an occasional rasping chuckle escaping his lips.

No known birth name. Mundane records hacked from the Gotham City Police Department showed that he had no known relatives, despite DNA testing. There were many hypotheses as to who he was. One theory suggested a former enforcer for one of the gangs of Gotham City by the name of Jack Napier. Another theory suggested a former chemical engineer and wannabe comedian who ended up being a dupe of the Red Hood Gang. He'd often played games with the staff of Arkham Asylum, giving plausible but contradictory pasts for himself.

Then again, did it really matter who he once was? In the end, all that mattered was what he was now. A monster, a murderer, a figure that made children afraid of clowns when they shouldn't.

They called him the Joker.

If you've never heard of him…well, the first thing I'd ask is what the hell are you smoking. But if you really are ignorant of him, well, allow me to elucidate. The Joker is a criminal, one of the worst based out of Gotham City, and that city has more than its fair share of criminals, particularly exotic ones. He's the Clown Prince of Crime, who inflicts his lethal and chaotic pranks on Gotham, one of his signature weapons being a type of poison gas that inflicts lethal laughter on its victims.

And I was being told to impersonate him.

I looked out the window, at the blighted urban landscape beyond. I was not looking forward to this. Not one bit…

I'm wondering, if you're reading this, how much you know of my life before this time. I know my friend Hermione wrote a series of books under a pseudonym, changing the names to a degree to protect us, and they tell a fairly accurate tale of what happened during my time at Hogwarts. Some parts were toned down, particularly in the earlier ones, or glossed over. But they don't tell you what happened afterwards. Of course, if you're from the magical world, well, you'd know something of my story, even if I doubt you know the truth.

When Voldemort fell…well, it wasn't a fairytale ending. I was a soldier, just coming out of a war. Dumbledore had shaped me into a soldier, an obedient pawn who did his bidding. True, he hoped I could survive to have a life afterwards, but his training was inconsistent, and I think he wanted me to be his successor.

Fuck that.

I hated politics. I hated much of Magical Britain, the nepotism, the snobbery, the sheer unfair nature of it all. It was magical for me when I first started out, but in truth, I realise that magic has this uncanny knack of amplifying the follies of people. The prejudice, the xenophobia, the patronising, the superiority complex…well, more of a simple. Magicals seemed worse than Muggles because the magic brought out their worst qualities. Voldemort's death hadn't gotten rid of the problem, it just removed the main unifying force. The Blood Purist's snobbery and xenophobia were still there. And so were other problems.

I was fined pretty heavily by Gringotts because of our break-in. The Goblins would have demanded my being handed over to them for execution if it weren't for the whole Horcrux saga. Ungratefuk pricks. People who say the Goblins are honourable warriors are full of shit. They believe honour only belongs to themselves, and financial warfare was a perfectly good form of war, which basically means royally sodomising people every way they can financially. In short, finding perfectly legal ways to rob you blind. Then again, they did see fit to give me a share of the vaults of a number of the Death Eaters I put paid to, spoils of war and all that, and I wasn't left impoverished, but I learned that my father had siphoned off or sold many of the family's assets to fund the Order of the Phoenix's war chest during the last war. I wasn't poor, I was still fairly rich, but still…the only reason I had that much money was that the Goblins were canny investors.

Ginny and I were fumbling our way through a relationship, but my duties as an Auror caused more than a little friction with her. Things had come to a head shortly before this trip to the US, in cooperation with MACUSA. I think she might leave me.

She was right, though. Not wholly, but…she said I would never be happy unless I had Voldemort to fight. Not wholly right, but I needed something to fight. I fought crime and inequality. Or at least I tried to. It's entrenched everywhere. Wizards are not unique in their folly. They're just amplified by magic.

Arrogance and hubris, for example, is a too-human trait. Wizards think it's justified, and yet, despite their vaunted belief in their own superiority…someone broke into Borgin and Burke's, and stole some rather nasty artifacts. Someone who happened to be visiting Britain at the time.

The Joker.

He made his getaway quite handily for someone who hadn't had much experience with wizards before. As far as I know, the only encounter he had with any magic user was with Zatanna Zatara. Then again, many of the wizards had grown complacent since Voldemort was stopped, and they wouldn't have believed a Muggle like the Joker could do them any harm. Considering the half a dozen corpses wearing grotesque rictuses that resulted in Diagon Alley, well, they learned differently.

I think that's why I was sent to Gotham. There were a number of reasons why. I was a poster child for the DMLE, being trotted out when something big happened. Sending me to the US was meant as a sign that the British DMLE was taking things seriously. And in truth, I think they wanted me out of the way while some unpopular legislation was being discussed in the Wizengamot. I think some were hoping the Joker would kill me, or else one of the so-called 'Rogues Gallery', the menagerie of villains Batman dealt with on a regular basis.

Well, I wouldn't be surprised, given the orders we got from above. You see, Gotham City doesn't have a DMLE or an Auror corps. Most wizards and witches have left Gotham due to the crime, considering Metropolis or New York to be safer bets. Any Aurors needed there generally came from the New York DMLE.

As it happened, after coming back to Gotham, the Joker decided on a holiday to Florida. The DMLE there, aware of what had happened in Britain, had captured him, and after the usual jurisdiction pissing contest, he was handed over to the New York DMLE. And from there, he was brought into our custody. Unconscious, of course, as the Joker was a notorious escape artist. And then, this plan was formulated…

Hermione and I weren't the only ones present. Luna Lovegood was peering at the Joker's face. Her usually dotty expression was uncharacteristically serious. "Unfortunately, leaving aside the Yanks going with an insane plan, there's not much we can do. Using Legilimency on him…well, it was worse than that time I tried LSD. Veritaserum did nothing either."

"Yeah, but…becoming the Joker?" I asked. "In a city where he's feared and loathed? I mean, if the Batman comes across me, what the hell do I do?"

"Use Apparition to get away from him," Luna said with a shrug. "Batman's one of those Muggles…sorry, they call them No-Majs here…who'd know about magic. I'd love to see Obliviators try to take his memories."

I chuckled at the thought. Most of the Aurors here in the US were arrogant. Then again, so were the ones back home. A Muggle who could kick their collective arses would bruise their prides so much, they would never be able to sit down again.

"Anyway, once we've confirmed Harleen Quinzell's whereabouts, we'll have you take the Polyjuice Potion and then drop you off close to her," Hermione said.

"Are the local Aurors liaising at all with the GCPD?" I asked uneasily.

"I don't know. MACUSA used to be even more isolationist when it came to dealing with Muggles of any stripe," Luna said. "Newt regaled me of tales of what New York was like in the Twenties. It makes Britain look warm and cosy and inclusive by comparison. If they are, then it's possible the Batman may be in the know. He's known to have a partnership with Commissioner Gordon, and of course, he's been fighting against the Joker for years. I think there's a cross-contamination of Wrackspurt breeds there."

Hermione and I knew better than to comment on this. Both of them were here on special attachment, as they weren't actually part of the DMLE back home. But I trusted them, Hermione was a damned good researcher and managed to find reference material so I could imitate the Joker's behaviour on short notice, and Luna…well, she was ensuring that this experimental Polyjuice Potion was safe. For a given value of safe, anyway. Undercover work was dangerous, even if you weren't going amongst Muggles who weren't paranoid about Polyjuice Potion.

I had dressed myself in the Joker's clothes, albeit after giving them a damned good wash. And replacing the underwear. I'd have to use the same brand just in case, but I'd be damned if I used anything that was in contact with the Joker's lower regions. Just the thought of becoming him squicked me out enough already.

Anyway, this version of Polyjuice Potion would last for a day from a single sip. I needed a flask like Barty Crouch Junior did when he was imitating Mad-Eye Moody, but I could improvise an explanation. Seriously, flying by the seat of my pants pretty much sums up my whole life.

Maybe that's why I was chosen for this, at least to imitate the Joker. He is chaotic and mercurial, and was as excellent an improviser as he was a planner. And he was an embodiment of chaos. To the hidebound idiots of the Wizengamot, so was I, sweeping in with reforms that were intended to ensure Voldemort or someone like him didn't arise again, or at least didn't seize power so easily. I was shaking up their ordered little worlds, and they didn't like that.

Or maybe it was my Marauder heritage. I chuckled softly to myself at the thought. If any of the Marauders were alive (save for Pettigrew, but he was no Marauder), they'd be laughing at me pulling one over on the most infamous prankster of modern times. I doubt the Joker would actually find it funny, though. His jokes rarely were, and he never liked it when the tables were turned on him.

It was that thought that bolstered my resolve to do this. If nothing else, royally screwing over the Clown Prince of Crime appealed to me. That, and ensuring dark magical artifacts remained out of the hands of a psychopath who wouldn't hesitate to use them. Say what you will about the Blood Purists and even some of the Death Eaters, but even they would hesitate to use these things. Not out of any notion of morality, mind you, but because they don't want to rock the boat they have a luxury cabin in.

And I've officially screwed up that metaphor.

Hermione's communications mirror emitted a chime. She made her excuses and left the room. She then came back. "Okay, Quinzell has been seen heading into the Iceberg Lounge. Graves just told me she's trying to get information from Oswald Cobblepot about Joker's whereabouts. It's showtime. Drink the Polyjuice, Harry, and we'll take you down there."

I nodded, before returning my gaze to the vial of Polyjuice, with some of Joker's blood mixed in. I remembered what Hermione once told me about what Julius Caesar said when about to cross the Rubicon, and thus spark off a civil war that would end with him in charge of the Roman Empire. Alea jacta est, I thought, before swallowing it.

I hated the sensation of Polyjuice Potion at the best of times. That sensation of your insides writhing like snakes, the burning and melting sensation as your very body changed. The fact that this Polyjuice Potion tasted the same way I imagined toxic waste-flavoured sherbet to taste didn't help matters. I couldn't help but scream in pain, a strangled cry.

And then, the cry changed into something more rhythmic, more frightening, all the more scary for the fact that it was involuntary. I was laughing, without any desire to. Just something born of compulsion.

I was becoming the Joker. Merlin help us all…

CHAPTER 1 ANNOTATIONS:

So, Harry's become the Joker to go undercover. This can only end well.

No numbered annotations this time.