The title already kinda gives it away, John Constantine is entering the stage. I had to rewrite his backstory to fit with Potter, considering that he is from the UK. So if anybody wants to complain about his backstory here being completely different than in in the comics, fine by me, I just wanted to explain the reasons for it.

"Never thought, I'd see this place again," said John Constantine as he got out a cigarette and put it in his mouth. The blond haired man, who could have basically been a clone of the singer Sting, wore a trench coat, a grey shirt, loose tie and khaki jeans. The only thing missing to make him look like the typical down trodden film noire detective come to life was a fedora hat.

"What place," asked his cab driver interested as John paid him his fine.

"The neighbourhood. Used to work here," John answered before knocking on the cab's roof to signal the driver that their business was done. He looked after the black cab for a moment before turning towards the small pub he was going to stay in. Carrying his single suitcase across the street, the wizard, or as he rather called himself, warlock, and detective opened the door to the shabby looking establishment.

It was a typical Monday afternoon with only five guests sitting at the tables, two of them having bags with them, indicating that they had just finished shopping at Diagon Alley. The school year was about to start, so John had expected some more patrons who had returned from a shopping spree. Not that it really mattered, John was not back here to meet anybody or to rekindle old relationships, let alone make new acquaintances as long as he could help it. He walked straight up to the bar where the old inkeeper, Tom, was standing and washing glasses.

"How can I help you?," he asked John, revealing several missing teeth by grinning friendly.

"I'd like to check in," replied John and pointed at his luggage. "Any rooms available?"

Tom nodded and got out a black book. "For how long will you stay, Mr...?"

"Constantine, John Constantine."

As he mentioned his name, Tom's head shot up and his eyes went wide. "I thought you had – "

"Died," John finished the question merrily. "Nope, just went to the US," he explained.

"What brings you back, if I might ask?"

"Work," John replied, not willing to discuss his personal business any further with the other man, who had not made any indication that he was going to look for a room from John. John leaned forward and stared directly into Tom's eyes. "Why did you think I was dead?"

"Because, you know, people talked," Tom replied in a hush voice. "That You-Know-Who asked you to join him and you refused. Nobody did that and survived."

"Well, I did. Screw the self-appointed aristocrat without a nose, that was my motto. And now give me my room," John said, putting a lot of emphasis on the last sentence, making it sound like an order.

Tom swallowed hard and did as he was told. "Room 19 would be available."

"Good."

"For how long will you stay, Mr. Constantine?"

"That depends on how well my business is going to go," John replied mysteriously. "Could you please take my luggage upstairs? I only have US Dollars on me right now, if you understand."

Tom nodded. "Of course. You still know how to get into – "

John waved him off and simply walked away, not even dignifying that question with an answer. He walked out into the backyard of the pub and got out his old wand. After tipping the right bricks the wall turned into an arc and revealed a familiar sight. John had left England nearly seventeen years ago, shortly after his eighteenth birthday. Once he had graduated from Hogwarts, Dumbledore had tried to recruit him into his little Order club, but John declined since he had just finished school and was not too keen to continue to keep all that much contact with his former teachers, especially not Minerva McGonagall. Since he had been a Slytherin and the second best of his year, he had known that it was only a matter of time until Lord Voldemort would come knocking. When that happened, John had already prepared everything for his escape. The self-proclaimed Dark Lord had offered him a position in his ranks but John had declined. He might have been an arsehole but he wasn't a cold-blooded murderer or psychopath, as he had told the noseless freak back then.

Voldemort had of course been pissed and obviously tried to kill John, but John anticipated that. When Voldemort shot his death curse at John, he simply apparated away. Everything that was important to him he already had send away or he was wearing on his person at that very moment, so when Voldemort, fuelled by his petty anger, destroyed John's house, John had managed to escape unscathed. But he has lived in an rented apartment and the explosion Voldemort had caused, killed several of his neighbours, all muggles, people Voldemort and his insane followers deemed completely unimportant. That his escape had cost eight lives had been a shame that John had not been able to live with. He started to drink and smoke, and after making it to America he did not return.

At first, the US had been nothing but a hiding place but in the end, it had kind of become John's home. He had always clung to his British heritage, drinking whiskey instead of bourbon, never trying to suppress his strong, native Liverpool accent, stuff like that, but he had never wanted to return to this country. If his girlfriend had not requested him to do a favour for a common friend, he would not be here right now.

After exchanging some of his muggle money for wizarding money – and after nearly two decades of living on the decimal system, it occurred to John for the first time, how truly ridiculous the monetary system in the wizarding world was – John went down Knockturn Alley. He knew these kinds of places like the back of his hand, even though he had only been in Knockturn Alley itself once.

As a private detective, John had been in many shady places, and the truth was that since he lived in Gotham City he had seen so many dark alley that even seemed to be dark in the middle of the day due to all the shadiness going on there, that he was getting sick of it. Borgin and Burkes was located at 13B and was easily recognisable as one of the bigger shops. It practically screamed "dark arts" and John had to shake his head about the fact that it, and many of the other shops here, had not been closed down yet.

As he walked down the alley, he had gotten many suspicious and even downright nasty looks for his attire. John did not particularly care and smoked a cigarette, further showing that he did not really belong in this place. When he entered Borgin and Burkes, John let his cigarette fall down inside and put it out with his foot. A bell rang, signalling his arrival and soon after a stooping man with oily hair appeared behind the counter. "How can I help you?"

"Who would you be?"

"What," asked the oily haired man confused.

"Mr. Borgin, or Mr. Burkes," asked John as he walked over to the counter, his hands in the pockets of his trench coat.

"I'm Mr. Borgin. And you would be?"

John smiled a sly smile. "Wouldn't you like to know," he replied. "I'm here because I want to have some information about a former employee of yours."

"Now, listen, sir, if you come in here – "

"Mr. Borgin, we can do this the hard way or the easy way. It doesn't really matter to me, and I think both of us know that you don't really like to involve the Ministry, do we?" This seemed to have shut Borgin up for now. "Where was I? Oh yeah, your former employee, a certain Tom Riddle, better known now as Lord Voldemort."

Borgin gasped. "You dare to speak the name of the – "

"Stop you right there. If you now call that dipshit the Dark Lord, I''ll see myself forced to break your nose. And don't even think about using that thing," John said as Borgin was reaching for his wand. The detective was way faster and had his already in his hand, pointing it at Borgin. "Now give that to me, will you?"

Borgin swallowed and handed John his wand, which John quickly pocketed away. "Here," he grumbled.

"Good boy. Now, Tom Riddle. I know he used to work here in the 50s. Why did he leave?"

"I don't know."

"You have to sound a little bit more convincing for me to believe it."

"But I really don't know. One day he went visiting a customer and the next day he didn't longer show up to work," Borgin pleaded.

"What customer?" When Borgin did not reply, John repeated his question.

"What do you offer me in return?"

John rolled his eyes. "Do you know any muggle entertainment?"

"No, of course not," Borgin replied, sounding disgusted at the very notion.

"Too bad," John said and grabbed Borgin at his collar, yanking him across the counter, thusly shattering some items that had lain on it. "Otherwise you might have seen this coming."

"Is this suppose to intimidate me? If I tell you what you want to know and he finds out, I'll have hell to pay."

John smiled a fake smile and let go of Borgin's collar. "Of course, I understand," he said and just as Borgin was about to get up again, punched him onto the nose with full force, knocking the other man backwards. In the last second, John grabbed Borgin's ear and twisted it so that he was once more lying on his counter. "I live in Gotham City, I deal with dirty bags like you all the time. And they are all afraid of the big guns. And you know what? I don't care. You tell me what I want to know or I'll introduce you to the guy, these big guns are all afraid off."

"Why should I be scared of a guy, muggles are afraid off?"

"Because it's not just muggles that piss their pants when Batman comes calling, which might have something to do with the fact that he is friends with literal gods. So, tell me, what customer did Riddle visit before he disappeared?"

"Hepzibah Smith. They met first time in '55, when she came here to sell somethin'. Burke wanted a goblin-made armour she had and she was really taken in by Tom, you know. And so he send her to her several times, and I think over the years they became friends. But then in '61, she died, murdered by her own house elf, two days after Tom had disappeared."

"And the day he disappeared, he had visited her," John asked and twisted Borgin's ear further, making the man squeal with pain.

"Yes."

"Thank you," John said and let go of the shop owner. "I hope we won't see each other again."

"Gladly," Borgin replied. "My wand," he asked just as John was leaving.

Without turning back, John dropped it onto the street just in front of the shop and walked back up to Diagon Alley, already having another cigarette in his mouth. He had no doubt that Borgin was going to follow him, or at least pay somebody to do so. But John didn't really care. He walked straight back to the Leaky Cauldron, signalled Tom that he was not going to go to his room right now, and left it directly for muggle London. John blended in pretty well with the usual crowd of pedestrians and just walked up to the closest café and went inside. From there he observed the Leaky Cauldron as he drank a nice, relaxing cup of black coffee, and smiled as he saw two women, dressed in dark, shabby robes leave the Cauldron, looking up and down the street. Everybody who noticed them, and it were actually quite a few, gave them a curious look but nobody said anything. This was London after all, a major city, and people wearing crazy close were not too much out of the norm.

The night had fallen and John was standing on top the building neighbouring the Leaky Cauldron. "Shabby little pub," said a dark voice from behind him.

John smirked. "Batman, you can see it?"

"Perception filters only work if you don't know that the hidden object isn't there."

"Good point," said John and took a swing from his flask before offering it to Batman who ignored the gesture as usual. "You know, you could have asked me directly for help."

"I called your number, Zatanna picked up," Batman explained stoic.

"Fair enough. And you're right, that thing is shabby."

"Any trouble?"

"Getting here or in there?"

Batman answered John's rhetorical question with nothing but a cold stare.

"I had to apply some pressure but Borgin did say something," John answered and told Batman what he had gotten from Borgin.

"Does the name ring any bells for you?"

John shook his head. "Nope. But I know one thing, Riddle killed her."

"Do you have any evidence for that?"

"No, but I doubt that a house elf would murder their master. Maybe if it was an accident but considering the connection to Voldemort, I'd find even that suspicions."

"Indeed," Batman replied. "Will you stay here or return to Gotham," he asked after some silence.

"I still got business with Voldemort," John replied, not going into details. "If you hunt him down, I want in."

Batman just looked at John and the wizard could just feel the penetrating gaze of the man behind the mask, but he would not buckle.

"I'm going to stay, no matter if you like it or not. So we can work together or on our own, but I'd say that together we stand a way better chance against that bastard. What do you say?"

John stretched out his hand and after a second or two, Batman grabbed it. "Don't let your feelings get in the way of this investigation."

"I can't promise nothin'," John quipped and walked towards the fire escape, leaving Batman alone on the roof. At least of a second, if he knew Bruce Wayne and his ability to disappear from one moment to another as if he could apparate himself.