The truth is, I don't own Batman ):

Oooh, I've been really nervous about posting this. I have completely immersed myself in all that is DC Comics, specifically those of which feature Joker and Harley Quinn. I admit I am a huge Batman geek, but mostly for the animated series and the Justice League, so my comic book knowledge isn't all that up to par. More notably, I have never written for the Batman fandom ever and haven't written a multi-chaptered on-going story in a very long. I'm sure you can appreciate my nervousness at posting this. I'm going to be honest; I'm relying heavily on feedback to know what I'm doing right and what I'm doing wrong both in my knowledge and my writing itself. I know that I can sometimes babble and become inconsistent. Mostly however, I hope you enjoy this as much as I am enjoying writing it.

I'm going to go out on a whim and say that it is painfully obvious that this is a crossover. Also, that the Dark Knight is fabulous and that I am unashamed to say I have saw it six times. :D.

00 Prologue.

It starts with a door knock and from there on, Harley finds herself being whisked away towards some new misguided adventure by Batman (really, she can hardly believe it either). "There's a problem on Earth forty-something." He says emotionlessly, and god Harley doesn't really care because she thought she was done with this multiverse mumbo-jumbo, hadn't she just gotten back from some other way-ward Earth? So his words come out as a chorus of "blah blah blah, problem problem, woe woe wooooooooe!" and she stifles a giggle because even if she is legally sane now, it's all rather amusing to her. Until Batman says the word 'Joker' and suddenly it's not funny anymore. Damnit, she was done with the Joker too, wasn't she?

Harley stops running on some roof of some building and so does Batman, and she processes the last twenty minutes in her head. The knock on her apartment door had sounded at exactly eleven o'clock because she had just come out of a two hour long soak in the bath. Hair laying limply across her face and neck, she had quickly tossed an over-sized tee shirt over head and stumbled towards the door where the knocks had become less patient and more urgent. "Yea, yea I'm comin'!" she had yelled before slipping her arms out of the two holes of her shirt, and opened the door. The temptation to slam it in his face was almost far too overpowering. Instead, she'd squeaked out an "oh".

"You," she'd said nervously, wringing the bottom of her shirt in her hands. "What do I, uh, owe this pleasure, Bats?"

Batman had just stared at her. "I need your help."

Harley stared back, her face straining to be cheerful and she stepped back. "Come in, come in." she twittered, not bothering to hide her nerves. "Sit down." She ordered tiredly, jabbing her thumb towards the small couch. She shuffled into her kitchen, poking her head round to the costumed man on her couch. "Whatcha drink Bats?"

"Nothing."

Swallowing, she'd brought her head back into the kitchen and nodded, frowning. "Nothin'." She mimicked quietly, pulling a face. She emerged moments later, a cup in her hand ('Holly' engraved onto it, Batman had noticed with narrowed eyes). She sat down beside him, placing her cup on the colourful coffee table she had insisted on buying. "So…"

"I need you to get dressed." He said immediately. "You'll need to pack, I'm not sure how long for, but enough for at least a few months."

"Right." She said, frowning, then snapped her head round to gape at him. "What do ya mean a few months?! Where the hell am I goin'?!" 'What makes you think I'll actually help you?!' she had wanted to scream too, but that she kept to herself.

"Once you're ready and packed, I'll explain on the way."

So here so she was, dressed in sweatpants and a hoodie, large suitcase in hand and staring at Batman with wide eyes. "Sorry, come again?"

Batman glances at the street below, and pinpoints which alley he has parked his bat-mobile. "There's a problem with one of the Earths." He says, folding his arms. "It's not one we are familiar with, but…" he trails off, and Harley sees him frown. "There's a Joker on that world who is out of control."

"Can't their Batman deal with him?" she says, her voice sounding a little too bitter.

"Not exactly." He grumbles his tone irritated. "The Batman from that Earth took the fall for Harvey Dent and his now Gotham's most wanted."

Harley can't quite hold back a laugh. "This Batman some kind of idiot?"

"He's young. All of them are – Harvey, officially is dead, but in reality he's locked up in Arkham. He hasn't established himself as Two-Face yet."

"So what's the problem with Mr. J?"

"He's in Arkham, but according to well…. The source who contacted me, he's being very difficult."

Harley raises an eyebrow. "So? What's that gotta do with me, Bats?"

"He's young Harley. A lot younger than you're Joker. Just started out, as far as I can tell." His tone his low and Harley starts to understand he's trying to persuade her. "Not quite the same, but the similarities are still there." He says and Harley thinks if he were a criminal there'd be a devious little twinkle in his blue eyes. "They need someone to figure him out, outsmart him."

"I ain't ever outsmarted Mr. J, Bats." She whispers, voice quivering. "And anytime I ever got close to, he'd always remind me that he delivered the punch lines." She shoves her hands into her pockets, suddenly feeling a little nostalgic.

"You've got an advantage with this Joker, Harley."

Harley stares at the ground and she doesn't need Batman to say anymore, she gets it. She's a smart girl, under all the blond hair and lazy attitude. She's got more than few years advantage with this new Joker. She's spent enough time with her own to know his quirks. His likes, his dislikes, when he's lying or when he's telling little parts of the truth. She knows his moods inside out, knows his mannerisms and his body language. She knows HER Mr. J, but she doesn't know this younger fresher Joker who isn't quite her own. But then, the foundations will be the same she guesses. His humor, the same. His reasons are probably the same and his motivation. And of course, his little obsession with the Batman. They're always a constant. He likes a laugh, likes to hurt people and really he just wants the world to laugh with him while he burns it.

Harley understands this new Joker will probably try to twist her head. Her heads already twisted round to his level anyway. She will infuriate him, but that's nothing new. He'll try to kill her, eventually, but Harley knows how to get out of that particular predicament quite well from all the years of practice she's had. But there's the small nagging doubt that she might just well… Be charmed all over again by this Joker. Then again, she might just have something for that problem too. Harley's spent enough time on her own, with new partners and friends, to have developed her own backbone and her own sense of purpose.

"So you want me to shrink this guy, huh." Her voice comes out like a squeak; not quite frightened but not quite sure.

"Something like that."

"Look, I'm gonna be honest with ya Bats. Mr. J, he ain't ever gonna change. The most I'll be able to do? Well… Get inside his head a little and then give Batman some tips."

Batman smirks. "It's enough."

Harley nods, butterflies in her stomach. "So how do we get there?"

"Our friend has some kind of device."

She laughs despite herself because she really must be crazy to be agreeing to this. Shakily she takes his hand while he uses his little gadgets to get them on the ground and suddenly she's in his car and they're driving and driving for what seems like hours to Harley until they're under caves and then… Well Harley isn't quite sure what to make of where they are. "You must've finally cracked." She squeaks, getting out of the car, case dragging behind her as she looks around the bat-cave. "Bringin' me here… Musta cracked good."

Batman glances at her, eyes narrowed. "No, it's a necessary step. Contact is made here, and so you travel from here." His voice is cold but Harley can hear the faint dread in his voice. "I-" he starts, then stops himself, mouth twisting into a frown, "the other Batman," he corrects, "will be waiting for you. Once you're there you can sort out your living arrangements with him."

An intake of breath is his response. Suddenly there's a million questions going through her head but she can't find her voice to ask them.

"This is a last resort." Comes Batman's voice, as if reading her mind. "You're not stupid Harley, you've proved that time and again. You've also proved how unstable you can be and how naïve you are in befriending extreme personalities." He glances back at his computer screen. "This is a last resort. I can't allow that Earth-" he stops suddenly, closing his mouth tightly.

Harley scrunches up her nose distastefully, not missing the little remark nodding towards her early years as an intern. "I get it," she states flatly, "I'm plan D."

Batman smirks at her. "Good."

"So, we getting this show on the road or what?"

Nodding, Batman points towards a metal archway that reminds Harley of old horror films. "Stand under it," he instructs, typing away at his computer.

"You sure this is safe?" she croaks.

"Yes. I've had it for a while… Just in case."

Harley thinks it's not at all surprising that Batman has something like this; he has everything else after all. Must be one rich fella'. She muses. Taking a gulp of air into her lungs, she grabs her case and marches purposefully towards the machine, standing as instructed. "Ready, B."

Batman doesn't say a word, just hits a few buttons and closes his eyes as flash of hot white light bathes the cave for at least twenty seconds. When it's faded, he opens them again, pulling off his cowl and running a hand through his hair, turning his chair to look at where Harley had previously been standing. Bruce lets out a shaky sigh. "Good luck, Harley."