Disclaimer: Harry Potter belongs to J. K. Rowling, and The Dark Knight belongs to Christopher Nolan/Warner Bros./whoever else owns it.
The first time the Joker saw Jim Gordon, the green-haired man was too far away for him to be able to make out any distinguishing features. He was standing near the Mayor, up at the podium. The Joker frowned, feeling the niggling sensation he got when confronted with something familiar. Usually it only occurred when something somehow came from his past, which was odd, seeing as just about everyone from before he became the Joker was dead, whether from his own hand or from others'.
He pulled himself away from his thoughts as the rest of the guards, fake and real, were called to attention.
'I've never killed a mayor before,' he mused to himself, all other thoughts forgotten as he focused on this new game.
The second time the Joker saw Jim Gordon was just as he was about to slip his fingers under Batman's mask and see who he really was. Gordon pulled him away with a gun to his head and the quiet words, "We got you, you son of a bitch."
He only saw a flash of his face before he was shoved facedown to the ground, but it still seemed familiar, as did the voice.
The green-haired man resisted the urge to start thumping his head against the ground in frustration that he had gotten to see neither the Batman's nor Gordon's face, content with the fact that soon everything would dissolve into chaos. He loved chaos. Order…
His face twisted. Order. That brought up memories. He hated those memories. He hated the word 'Order.'
The third time was as he was sitting in a holding cell in the MCU. Gordon came in, looking tired. He conferred quietly with his officers about the green-haired man, but the Joker could hear everything. He had sharp ears, honed by a past of whispers, quiet voices, and danger.
He laughed quietly on the inside as they talked of his knives (oh, how he loved them), his custom clothes (he didn't want to conform to social norms, and if he was going to do something like this, why not go all the way and be completely original? Besides, all the money he had inherited could be put to use buying them), and how he had no apparent past (he had one, but he thought of it as little as possible, and it wasn't like these idiots would have been able to find it anyway). Then the Mayor came in and announced that Gordon was the new Commissioner. Interesting.
Still, that voice. It was so familiar. He needed to know who it was that Gordon reminded him of, so that he could kill the Commissioner – Gordon was driving him mad, and he crushed any inadvertent reminders of his past.
To his frustration, despite everything he had been through in his life and the contacts he was wearing, his eyesight was still a bit too blurry to be able to make out fine details at a certain distance. He could see Gordon quite well, but he couldn't check for the exact details needed to be able to compare it to the person the new Commissioner sounded and looked slightly like.
The fourth time the Joker saw Gordon was after he had left and come back. The green-haired man was sitting in the half-dark interrogation room where they had left him shortly after calling the Commissioner.
"Evening, Commissioner," he drawled out, eyes quickly taking in the man now that he was close enough for the Joker to be able to see in complete detail.
"Harvey Dent never made it home," Gordon said quietly, sitting down in front of him.
"Of course not," the Joker said, smiling slightly. The grin slid down his face as suddenly the pieces all clicked together. It was the way that the light fell on the Commissioner's face that clinched it. His face looked slightly gaunter in the half-light, his eyes darker. Despite the moustache, shorter hair, and glasses, the Joker could see the familiar face underneath. And now that he thought about it, Gordon had a very slight British accent in his speech.
This wasn't possible. He had to test him. "You wanna know how I got these scars?" he asked, leaning forward and staring straight into Gordon's eyes.
Gordon's expression tightened and his eyes narrowed in anger as he stood. "I don't have time for your games," he said, unlocking the Joker's cuffs and starting to head towards the door.
"Your cousin Bellatrix is a real bitch, you know that, Padfoot?" the Joker called.
Gordon froze. Very slowly, he turned around.
"How do you know about her?" he breathed. "And that name?"
The Joker smiled and spread his hands. "I'm hurt you don't recognize me," he said. "Then again, the years change everyone. It's no surprise, honestly – I'm so different from how I used to be, I don't know who would recognize me." He let that sink in for a moment, and then said conversationally, "I didn't know that you thought Lily was a bitch, though. Merlin, Snuffles, I hope you never said that to her face!"
Sirius had always been a smart man. Otherwise, how would he have been able to become an Animagus at age fifteen, without any adult supervision to help? The Joker watched as Gordon processed the information dump, and then connected the last two sentences with what he had said several hours ago. He paled suddenly and almost swayed where he stood.
"Harry?" he whispered, eyes wide.
The Joker laughed loudly. "I haven't been called that in years!" he said, ignoring for the moment the bitter memories surfacing. "I'm so disappointed you didn't recognize your own godson, Padfoot!"
Gordon flinched, and the former Boy-Who-Lived imagined he could hear everyone on the other side of the glass they were examining them through take in a breath of disbelief. His everlasting grin widened.
The Commissioner sat back down at the table, peering into the Joker's emerald eyes as though trying to see the truth of what he was saying. For a brief moment, his gaze flickered up to the Joker's forehead, but he had always covered that section particularly well, and was certain Gordon wouldn't be able to see anything there.
"What happened to you?" Gordon asked.
"Life, and time, and war," the Joker said. "And Bellatrix," he added. "She got all pissy when I killed her master and was so sad over my friends and comrades having died. 'The Gryffindor Golden Boy shouldn't be so saaaaad...' she said. 'Let's put a smile on that face!' Of course, I killed her right after," he said, shrugging unconcernedly.
"He's dead, then?" Gordon questioned after a brief moment of disgust in the utter nonchalant way his godson had talked about having his face cut open.
"Oh yes," the Joker said gleefully. "He's very much dead. I've danced on his grave." His eyes twinkled merrily. "Of course," he continued with a slight downward turn of the lips, "I didn't kill him until he had already murdered all the fighters, including me. Essentially, we lost the final battle, even if we did technically win the war."
If Gordon was confused, he didn't show it. The Joker hadn't explained anything, really. "What happened to you? What made you like…this?"
The Joker leaned forward. "You're telling me you hadn't been driven mad with grief when you finally caught up to Peter? I've been driven mad, but it stuck around." He sighed suddenly, leaning back some. "Go rescue your new Saviour, Sirius. I am growing tired of this game, this city. The world's no fun anymore…there's no good competition. Everyone has morals, and I'm not ready to deal with too many goody two-shoes. She's at 250 52nd Street, and he's at Avenue X and Cicero."
"She?" Gordon asked, already standing. His gaze flickered to something behind the Joker.
"Rachel Dawes," the Joker shrugged. He made little shooing motions with his hands. "Go on. The clock's ticking, Gordon. By my estimates, you have…ooh, ten minutes, maybe?"
"Shit!" Gordon turned and strode quickly to the door.
With a slam, the Joker's head hit the table, and he lifted it in time to see Batman going with Gordon. He laughed.
Through his laughs, while he was cradling his head and blinking his eyes, he called out, "Don't worry, Sirius! I'll stay here and we can have a looooong discussion of what's happened over the past few years!" He cackled loudly.
Despite what he'd said, maybe he would stick around this city for a while longer. At the very least, he'd have to pop back in occasionally to check up on his godfather.
Still laughing weakly, the Joker leaned back in his chair contentedly, eyes bright with merriment, lips and scars curled up in amusement.
A/N: This hit me with the force of a snowball to the back of the head today as I was attempting to build a snow fort (it snowed a good 12-15 inches here). I was thinking about how I've read a couple of fics where Sirius was the Joker, and one where he was Gordon (because they're both played by Gary Oldman), and then…this idea popped up.
Obviously, this is very AU. The Final Battle at the end of the seventh book went differently. Pretty much everyone at Hogwarts who was fighting died (including the members of the Order of the Phoenix who fought, thus Harry not liking the word 'Order'). Bellatrix stayed alive long enough to take her revenge on Harry after he killed Voldemort. Harry went mad with grief, became the Joker, and left the Wizarding World. He has been blatantly ignoring all the memories from his teens.
As for Sirius, when he passed through the Veil, he was dumped somewhere with amnesia, no wand, and most of his magic gone is what I'm thinking. By the time he's regained all his memories, it's been many, many years. I know that the timeline for this is all wacky. Just pretend a lot of years have passed. (By the way, I like the sort-of-not-quite-irony of Gordon being a good, fair cop in a city of bad ones when as Sirius Black he was tossed in prison by bad Aurors/judges).
The Dark Knight events will obviously be very different from what they were in the movie because of what has just happened, so that doesn't really need explaining…oh, and I didn't forget about the bomb. Harry just isn't going to set it off now. He wants to hang around and talk with Sirius, and while he could do that if he escaped, he's assuming that a) Gordon will be too well protected to attempt that any time soon, and b) he can pull together a plan to escape any time, so it probably doesn't matter.
Oh, and yeah, he did actually give out the correct addresses (he didn't feel up to trickery with his godfather, and some part of the saving-people-thing reared its head from where it had been buried long ago to give out their real locations). Also, they have a bit more time (maybe) than they did in the film to rescue them. So who knows where that's gonna go? Well, maybe me…I may or may not continue this. I certainly like the idea, and it's fairly original (I think), but it all really comes down to if people like it or if I'm motivated enough to continue it.