A/N: Lucifer Supernatural crossover!!! Why has this not happened yet?

Sam and Dean were working a case, and it happened to lead them to Los Angeles.

And seeing as they arrived a little late to hit up a crime scene and inspect a corpse, the boys headed to the local police department to get an autopsy report.

But they were in for a few nasty surprises inside the L.A.P.D.

A blonde woman in a pants suit stopped them near the door.

"Can I help you?" She asked. The Winchester flipped out their FBI badges.

"I'm Agent Torres," Dean began. "This is my partner, Agent Lane; we're here on the Adams case?" The woman nodded.

"The homicide case," she agreed. "I'm Detective Decker, I was assigned the case here- we don't have much information to go on yet, unfortunately."

"Do you have an autopsy report on the vic?" Sam asked.

"Yeah, our forensics team was right on that. Come on," She lead the boys further into the P.D., and poked her head in the forensics office. "Hey Ella, do you have the autopsy for the Adams case? We've got a couple FBI guys that need to take a look at it."

"Sure!" Ella said cheerfully, grabbing the report. She turned around, her eyes landing on the Winchesters, and she promptly dropped the papers.

Sam and Dean's eyes widened, recognizing the woman before them. Sam opened his mouth to speak, but Ella beat him to it.

"No," She declared. "No. No no no, You can't be here."

"How are you-" Dean started.

"But we saw-" Sam whispered. The three of them stared at each other, and Chlor glanced between them, confused.

"Do you know these guys?" She finally asked.

"Ye-" Dean started.

 "NO!" Ella declared. "No, nope, not at all, don't worry about it," She practically shoved Chloe out of the Forensics office and slammed the door shut behind her, whipping around to stare at the Winchesters. "Why are you here?" She squeaked.

"How are you alive?" Sam demanded. "We thought Lilith killed you."

"I DON'T KNOW!" Ella said, panicked. "There was a little girl, and she just murdered everyone. Everyone! She attacked me and I played dead, but then I didn't die, and just- You can't be here!"

"Why not?" Dean questioned.

"Because nobody HERE knows about THAT! They'd think I'm crazy! And maybe I am. After all, I think some little girl went around and murdered everyone. That's insane, right? I'm insane."

"It wasn't a girl. It was a demon." Sam explained. "Her name was Lilith."

"Oh, like that makes it better? Don't tell me she's here. She's here, isn't she? She found out I survived, and now she's come back to kill me."

"Lilith is dead," Dean assured her. "You're not in danger here,"

"I have to be if you two are here."

"That's not-" Sam sighed. "Look, we're just going to take care of this case, and then we'll leave and you'll never hear from us again. Alright?" Ella hesitated.

"Alright," She reluctantly agreed.

****

Outside the forensics office, Chloe tried to look in, confused.

"Detective!" An accented voice called out. She turned, only to see Lucifer walking up, smiling smugly as always. "I hear we have a new case."

"Yeah," Chloe said. "But there are a couple of feds working it too, so it looks like we'll have company."

"Oh?" The door to the Forensics office swung open and Sam and Dean walked out. Lucifer froze at the sight of them.

"Speaking of feds," Chloe offered. "Boys, this is my partner, Lucifer Morningstar. Lucifer, this is-"

"You have got to be kidding me," Lucifer declared, staring at them. Sam's eyes widened and Dean narrowed his eyes.

"Lucifer," Sam echoed.

"Long time no see!" He replied. 

"You son of a bitch," Dean muttered. Lucifer barely got another word in before Dean punched him in the face and Lucifer's head snapped to the side.

Dean hadn't expected it to do any damage. He had punched angels before, and all it had done was make his hand feel broken. Punching Cas was like slamming your fist into a cement wall.

And yet that didn't happen when Dean punched Lucifer. Satan's head snapped to the side, and he clutched at his jaw, his nose starting to bleed a little. Sam and Dean's eyes widened at that.

"What was that?!" Chloe demanded, whipping towards Dean.

"No, no, I deserved that one." Lucifer admitted. Dean punched him again, and Lucifer nodded. "That too."

****

A few minutes later, they were sitting around Chloe's desk as she tried to determine how they all knew each other.

"Here's the short version," Lucifer offered. "My brother is basically married to him," He pointed at Dean, who glared at him in return.

"Your brother?" Chloe echoed. "Which one?"

"Castiel,"

"How many brothers do you have?"

"Hundreds. Anyway, Cassie and I don't exactly get along,"

"If by that you mean last time you saw him you STABBED him in the back," Dean snapped. "Literally and metaphorically."

"I didn't know you knew the word metaphorically," Lucifer grinned. "So, naturally, Dean here hates me."

"I have plenty of reasons to hate you. You've only singled out ONE." 

"Got it," Chloe offered. "But how do you two know Ella?" Lucifer's ears pricked up.

"You two know Ms. Lopez?" 

"That's....confidential information," Sam said slyly. "Don't worry about it."

******

The Winchester were not pleased to find out that Lucifer was living in L.A. and working WITH the police, of course.

So while Sam and Dean dug into research about their case, they sent Cas to investigate everything Lucifer related. And fortunately for Cas, Lucifer hadn't exactly kept a low profile in this city.

The path led Cas to a therapist's office, of all things.

"Can I help you?" A blonde woman asked him.

"Are you Linda Martin?" Cas asked, tilting his head.

"Yes,"

"I need to ask you some questions about Lucifer Morningstar," Cas fumbled for his fake FBI badge, only to discover that he'd forgotten it. 

"Lucifer?" Linda echoed. "Well, I can't break patient confidentiality... Who are you, anyways?" Cas sighed. If Lucifer hadn't been lying in this city, maybe it would be best for Cas to just tell the truth for once.

"I'm his brother." Linda's eyes widened.

"So... You're also an angel?" she squeaked. Cas blinked. Lucifer really HAD let everything go in this city.

"Yes."

"Which one? Michael? Raphael? I don't really know any more-"

"Castiel." Cas interrupted before Lina could compare him to anyone else hideous. "My name is Castiel."

"Oh," Linda paused. "Lucifer never mentioned you..." Cas scowled.

"Of course he didn't. Why would he ever talk about the brother he stabbed in the back and murdered. I bet he hasn't told about Gabriel, either, has he?"

"Why don't we take this into my office?"

******

Three hours later, Castiel, Lucifer, Sam, and Dean were all reluctantly sitting in Dr. Linda Martin's office.

"You KILLED your brother?" Linda demanded.

"It's not like it was my fault!" Lucifer objected. "He was just... in the way!" Dean fought back a growl.

"Like how Gabriel was just in the way, so you had him CHAINED UP AND TORTURED?" Sam snapped.

"Sam, you've been tortured by me before. I think we can both agree that Gabriel can handle it."

"I hate you!"

"Join the club," Dean muttered.

"So, I'm sensing a lot of tension in the room," Linda began.

"Oh, sorry," Cas apologized. "That'll be from me and Dean. Sam's always complaining about our sexual tension." Lucifer and Dean slowly turned to stare at Sam.

"When you two fuck, I'll shut up." Sam said firmly. Linda looked unsure if she should ask about that topic, and Castiel's glance confirmed that it was not something that should be mentioned.

"I'm sure the fact that I've been inside Sam doesn't help this conversation," Lucifer said smugly.

"Oh my god," Sam covered his face with his hands.

"To clarify, he possessed him." Cas piped up. "And me, technically."

"Who's to say I wasn't referring to having sex with him, Cassie?"

"You didn't have sex with Sam Winchester."

"How would you know?"

"Because you DIDN'T!" Sam agreed. "Dean's the angel-fucker, not me."

"Two angels." Dean muttered. "You screw TWO angels, and they NEVER let you live it down."

"Are you ever gonna let me live down Ruby?"

"Hell no."

"EXACTLY."

"Who's Ruby?" Linda asked.

"A demon." Sam supplied. "Long story."

"One of Maze's old friends, actually," Lucifer grinned. 

"Maze never mentioned any old friends..."

"She never mentions things."

"Try asking her what happened to Crowley," Dean glared. "See what happens."

"Hey, Crowley killed HIMSELF, that was NOT my fault-"

"YES IT WAS, FUCK YOU." Dean, Sam, and Lucifer exploded into an argument while Cas just stared pitifully at Linda.

"I just want Dean to kiss me," He said. "That's all I want to get out of this." Linda nodded slowly.

"You three are leaving town soon, right?" She asked. Cas nodded frantically.

"Definitely."