Watch The Road So Far because what's a season finale without it?

On April 21, 1967, the 100 millionth GM vehicle rolled off the line at the plant in Janesville – a blue two-door Caprice.

There was a big ceremony, speeches. The lieutenant governor even showed up. Three days later, another car rolled off that same line. No one gave two craps about her. But they should have, because this 1967 Chevrolet Impala would turn out to be the most important car – no, the most important object – in pretty much the whole universe.

She was first owned by Sal Moriarty, an alcoholic with two ex-wives and three blocked arteries. On weekends, he'd drive around giving Bibles to the poor "gettin' folks right for Judgment Day." That's what he said. Sam and Dean don't know any of this, but if they did, I bet they'd smile.

After Sal died, she ended up at Rainbow Motors, a used-car lot in Lawrence, where a young marine bought her on impulse. That is, after a little advice from a friend. I guess that's where this story begins.

And here's where it ends.

Libby pulled the car into Bobby's Junkyard, killing the engine. Nadia glanced out the window. "Where are we?" she questioned, never keeping her eyes on the same spot for more than a second. But Libby stared at the Impala with a smile.

There was Sam Winchester, drinking a beer, on the hood of the black 1967 Chevrolet Impala. Dean walked over, joining his younger brother on the hood of the car. He bent down and pulled a beer out of their old cooler, leaning against the Impala's side.

"Home," Libby replied. She opened the door and got out, Nadia copying her movements.

"I didn't realize you managed to make a home in less than a year," Nadia replied, following Libby towards the house. Libby shook her head.

"My home is more like a few people than a place. I may not be their home, but they're mine. They took me in despite my title. I was just an ally," Libby explained, stepping over a scrap piece of metal that was left stranded in the gravel. "But after months of hunting monsters with them, I found a home in them. They changed me." Nadia nodded in agreement.

"I've noticed. And here I thought it was just Hell."

"No. Hell didn't do anything to me. It was the Winchesters." Libby and Nadia fell silent as they continued to make their way towards the Impala instead of the house.

Dean glanced down at his beer, sighing. Sam looked over.

"Dean?" Sam asked. "What's going on?"

"I'm in," Dean said curtly. Sam looked at him in confusion.

"In with...?" he trailed off, not knowing what to think. Dean popped the cap off of his beer.

"The whole 'up with Satan' thing. I'm on board," Dean clarified. Sam sat up, staring at him in shock.

"You're gonna let me say yes?" Dean shook his head.

"No. That's the thing." Sam just stared at his brother, confused. As did Libby. She held out her hand in front of her mother, signaling Nadia to stop. Libby wanted to hear what was going on before she just barged in.

"It's not on me to let you do anything. You're a grown – well, overgrown – man. If this is what you want, I'll back your play. Besides, we owe it to Libby, right? Who knows what happened to her. Maybe Lucifer killed her, maybe some demon killed her. Hell, maybe she even sided with them. I don't know. But what I do know is that I shouldn't have acted like that to her. She was just helping," Dean explained.

"That's the last thing I thought you'd ever say," Sam admitted.

"Might be. I'm not gonna lie to you, though. It goes against every fiber I got. I mean, truth is... You know, watching out for you... it's kinda been my job, you know? But more than that, it's... it's kinda who I am. You're not a kid anymore, Sam, and I can't keep treating you like one. Maybe I got to grow up a little, too. I don't know if we got a snowball's chance. But... But I do know that if anybody can do it... it's you."

"Thank you," Sam replied.

"If this is what you want... Is this really what you want?" Sam sighed, thinking about it for a moment.

"I let him out. I got to put him back in," he said. Libby watched in shock. Sam was going to say yes and try to overpower Lucifer. Could he even do that?

"Okay. That's it, then," Dean said. He leaned back against the Impala. Libby took this as the chance to intervene. The gravel crunched beneath her boots as she stepped out from behind the car.

"You know, I've see stupid. I've seen thousands of years worth of stupid, but I've never seen anything quite this ridiculous," she said. Sam and Dean looked up at the sound of her voice, eyes widening.

Sam's gaze instantly fell to the tears in Libby's clothing, the blood stains that took over most of them. Libby looked strong, but her clothes looked like she had just crawled out of Hell again.

"Libby," Sam breathed. He set his beer down on the hood of the Impala, jumping off and racing over to the girl. He engulfed her in a tight embrace, Libby instantly hugging back. "I don't understand. We haven't heard from you in months. Everyone thought you were dead." She shook her head, resting it on Sam's chest. They stood there like that, in each other's arms, for a few minutes before Libby pulled away.

"My father took me. Tortured me to try and get me to help him. I never broke. I couldn't. I owed you guys that much." Libby sent a smile towards Dean. But his gaze was locked on something behind Libby. Something he recognized all too well.

"I thought she was a hallucination," Dean called out. Libby turned around to see her mother watching the three hunters in curiosity. Libby smiled slightly, shaking her head.

"Her name is Nadia. She's my mother." Sam and Dean both stared at the the mother and daughter in shock. "She helped me escape," Libby said. Nadia walked up to them, stopping in front of Sam first.

"You seem close with my daughter." His posture went stiff and he nodded.

"Y-yes, Ma'am." Nadia raised an eyebrow.

"And what are you to her? Ally? Friend? Lover?" Dean chuckled, earning a curious glance from Nadia. He walked over to the two redheads and Sam, taking a sip of his beer.

"I think lover would fit the description, right, Sammy?" Dean said with a grin, slapping his brother on the back. "According to Cupid, Sam and Libby are soulmates." Nadia eyed Sam, studying him up and down.

"You're big," she noted. Sam shifted his weight on his legs uncomfortably.

"Uh...thank you?" Libby snickered. "I'm not exactly sure how to take that."

"It's a compliment. You're strong, both physically and mentally. I can sense it. I can also tell that you're being stupid, but it doesn't take an angel to know that," Nadia replied. Libby glared at her.

"Mother!" she hissed. She nodded her head towards the car. "Go wait in the car. I need to talk to them." Nadia spared one last glance at the boys before turning and walking off towards the stolen car. "Sorry about her," Libby apologized.

"It's alright. I'm just shocked that she found you. No one was able to find you," Sam told Libby. Libby sighed, nodding. When no one came to her rescue she knew that she was warded somehow. She didn't know exactly how, she just knew that she was screwed until the warding broke. "Are you okay?"

"Yes. Better than okay, actually. I'm stronger. I was knocked out for a few months apparently, but that gave me time to heal. Sam, you can't say yes. We can take down Lucifer another way. I promise." Sam shook his head.

"I'm gonna leave you two to it," Dean announced, walking towards the house. He disappeared through the door, leaving Libby and Sam alone. They were hidden from Nadia's sight, giving the two some privacy. With the first chance he got, Sam dipped his head down and kissed Libby. She kissed back instantly.

"I'm so gonna miss that," Sam whispered against her lips. Libby pushed his chest slightly, pulling away.

"You don't have to."

"What's your big plan, Libs? The Colt failed, what makes you think the sword will work?" Libby shook her head. Throughout the whole drive to Sioux Falls, she was coming up with several different plans in her head until she decided on one. It was complicated and risky, but better than risking Sam's life.

"Not the sword. The sword won't kill him. It'll only kill me. But there's something else." Sam tilted his head to the side, confused. "He needs you as his vessel, right? What if we manage to convince him to use me instead?"

"Would the even work? It doesn't fit the m.o. You're not a sibling, Libby. You're just his daughter. You were a backup weapon," Sam said. Libby shook her head.

"No, you don't understand. Okay, I possess you, Lucifer possesses you which means he'd possess me. I know you have all of the rings now, Sam. You'd open the Cage and I'd pull us out of your head and into the Cage. Except I push him in and I do my best to escape before it sucks me in, too," she explained. Sam took a minute to process everything before he shook his head. Libby's face fell. "I'm not letting you throw yourself into the Cage. How do you even know you can overpower him?"

"I just do, okay?" Libby started to pace, biting her thumbnail in the process, as she thought up another plan. She stopped pacing suddenly, something she only does when she came up with a solution. "What? What is it?"

"He doesn't know my mother's back," she whispered in realization. "He loved my mother, Sam. She was the one who drifted away. He loved her so much that he rebelled to get her attention. He knew the consequences and he still did it. Nadia's our best option, Sam. I'm not losing you."

"Libby, it's only been a little less than a year since we met. I think that you'll get over me," Sam assured her. Libby sighed.

"Sam, I'm not worried about getting over you. I've lost a lot worse. I'm worried about you in that Cage with him. I know my father and what he does...it isn't pretty. If you think Dean going to Hell was bad, imagine being trapped in a Cage with Lucifer for all of eternity. I've done it before, and I would do it again if I needed to. Let us use Nadia. Please. We'll call you Plan B." Sam glanced at the house where Dean watched from the window, curious as to what they were talking about. Libby never took her eyes off of Sam. "Sam, please."

"You want me to what?" Nadia yelled. Libby rolled her eyes, following the Impala down the dirt road.

"You heard me."

"Libby, that man is a monster."

"And that man is the reason I was banished to Hell for no reason. That man is gonna be the reason Sam dies. Mother, this is the only way. I'll be right there with you to protect you. I promise. Please do this for me. Not for anyone else. Not for the world. Hell, not even for God. Do it for me. I love you, Mother, I really do. And I know that deep down you love me, too. You're our last chance at locking him away for good," Libby explained. Nadia was quiet for a few minutes, thinking it through.

"All we're doing is talking?" Elizabeth nodded.

"I need you to distract him long enough for us to throw down the rings and say the spell before I shove him in. It should be easy enough." Nadia sighed, nodding. Libby breath a silent sigh of relief. Sam didn't have to lock himself in the Cage to rot away. "Thank you."

"Don't thank me just yet. I haven't done anything. So I'm guessing we go to Lawrence now?" Libby shook her head. "But-"

"But no. Lawrence is where the battle between Michael and Lucifer is supposed to go down. Lucifer's in Detroit." Libby scoffed. "Of course he's in one of the most dangerous cities in America. I mean, why wouldn't he be?" Libby flipped through different radio stations before settling on a classic rock station, letting the music blast out of the speakers to fill the silence of the car.

Libby and Nadia followed behind Sam and Dean as they walked up to the building that Lucifer and his demons were hiding out in. Sam, high on four gallons of demon blood, raised his hands as he yelled out, "Alright! We're here, you sons of bitches! Come and get it!" Nadia sent Libby a disapproving glance, earning an eye roll from Libby. Two demons stepped out of the building.

"Hey, guys," Dean greeted. "Is your father home?" The demons latched onto Sam and Dean, shoving them inside and up the stairs. Libby and Nadia followed, Libby's hand never leaving the hilt of her sword the entire time.

"Stay calm," Libby whispered to Nadia, glancing down at her shaking hands. "I won't let him hurt you." Nadia nodded, managing to stop her hands from shaking.

Her heart still raced and the adrenaline still rushed through her veins. But she let her daughter's words echo throughout her mind. Stay calm. I won't let him hurt you. The demons, three hunters, and the angel all stopped in a room, greeted by the sight of Lucifer staring out the window.

"Hey, guys. So nice of you to drop in," Lucifer said. Libby nudged Nadia, gesturing for her to shove her way past the demons. Nadia did just that, Libby standing behind her and off to the side, ready to attack when needed.

"Lucifer." The devil froze, tensing at the voice he thought he'd never hear again. He slowly turned around, coming eye to eye with Nadia. "What are you doing? This isn't you," Nadia whispered. His eyes widened.

"Nadia," he breathed. She took a step closer to him.

"Stop this. Stop it now. These boys don't deserve this. Our daughter doesn't deserve this. No one deserves this. Why are you doing this?" Libby had to admit, she didn't think her mother had it in her. But Nadia was doing pretty good so far.

"You don't understand, Nadia. It's my destiny to fight Michael," Lucifer replied, still shocked that he was talking with the woman he once loved.

"Like it was Elizabeth's destiny to become a warrior? Look at her." Lucifer glanced over at his daughter as Nadia pushed a strand of hair behind her ear. "She was pure, the definition of perfection, until you rebelled. We can fix this. We can make things go back to the way they used to be. The three of us as a family. Elizabeth and I can forgive you. We can all be happy again." Lucifer stepped towards Nadia until they were inches apart. Libby heard Nadia's heart race. Not now. Hold it together.

"You're scared," Lucifer whispered in Nadia's ear, tracing her cheek bone. Nadia breathed in a shaky breath. Sam and Dean exchanged glances. They may have to use Plan B. "If you still loved me, then why would you be scared?"

"Can you blame me? The things I've heard about you...they can be forgiven but they still scare me," Nadia lied. The grip on Libby's sword tightened when she saw a demon advance towards her. "Please, Lucifer. End all of this." Lucifer stepped back, staring at Nadia, before reaching into his pocket. Libby pulled her sword out of her sheath, pointing it at her father. He glanced over at her with an amused smile.

"If you even think about killing her-"

"What? You'll kill me? Isn't that what you're here to do?" Libby didn't reply. "I don't know how you escape, nor do I care, but I do know when Nadia is lying. I loved her, remember? I knew everything about her. I also know when she lies. I'm the one who taught her that." Nadia gulped. Libby managed to step in between her parents.

"You'll have to kill me before you kill my mother," she said lowly, searching his eyes for any sign of humanity. Her plan had failed and she knew it.

"That's a stupid move considering you're holding the one weapon that can kill you." Libby nodded her head to the side. "I see the Winchesters changed another thing about you, Elizabeth; you're stupid. Stupid enough to think that Nadia would work. I know you have the rings."

"I don't know what you're talking about," Libby lied. Lucifer nodded, impressed.

"The Horsemen's rings? The magic keys to my Cage? Ring a bell? Unlike your mother, you're good at lying. You're great at it, actually. But, see, I have my spies and I get my intel." Lucifer looked up at Sam, his attention no longer on his daughter. "Come on, Sam. I've never lied to you. You could at least pay me the same respect. It's okay. I'm not mad. A wrestling match inside your noggin... I like the idea. Just you and me, one round, no tricks. You win, you jump in the hole. I win... Well, then I win. What do you say, Sam? A fiddle of gold against your soul says I'm better than you."

"Sam, no," Libby said. She shook her head. "You can't do this."

"Shut up, Libby," Sam said. She glanced over her shoulder and shot a glare at Sam.

"Yeah, Libby. Shut up," Lucifer mocked. He shoved Libby and Nadia out of the way, walking over to Sam and Dean.

"Mother, go," Libby said softly. Nadia looked to her daughter with wide eyes. "Go. I'm not gonna tell you again. Go to Bobby and Cas and tell them what's going on." Nadia nodded and raced out, no demons bothering to chase after her. That left Sam, Dean, and Libby all standing with Lucifer and his demons.

"So he knows. Doesn't change anything," Sam said.

"Sam," Dean tried.

"We don't have any other choice."

"No," Libby said, walking over to Sam. She placed a hand on his shoulder but he shrugged it off.

"Yes," Sam said, directing the answer at Lucifer. Libby's eyes widened as a bright light engulfed the room, Dean shieling his sight.

Bobby, Castiel, and a frantic Nadia all watched the light take over the room from outside before it dimmed down. "It didn't work," Nadia whispered. Cas and Bobby ignored her. They had most likely just lost Sam.

Dean and Libby looked around the room before the saw Sam lying on the floor next to the demons. Without hesitation, Libby ripped the rings from Dean's pocket and threw it against the wall, watching them stick. "Bvtmon...Tabges...Babalon." Suddenly a hole appeared in the wall where the rings were, air getting sucked into it. And if anyone were too close, they would be sucked in, too. Sam came to, looking around a bit confused.

"Sammy!" Dean yelled out over the howling of the wind. "Sammy!"

Sam let out a painful groan. "I can feel him. Oh, god!"

"You got to go now! Come on!" Dean helped Sam up off the ground. "Go now, Sammy. Now!" Sam walked over to whole, sucking in a few deep breaths. When Libby saw the slight smile on his face her eyes widened. That wasn't Sam. He turned around to face Dean.

"I was just messing with you. Sammy's long gone," Lucifer said. He turned to look at Libby, smirking at her. "Didn't you say you'd go back to Hell if it meant defeating me? How about if you went back without defeating me?"

Libby swung the sword, sending it straight through Sam's stomach before yanking it out. Lucifer just looked down at it. "Ouch." Libby knew what he was about to do so she ran, except Lucifer grabbed her arm. Libby let out a scream, kicking at Sam's body to try and knock him into the Cage.

"Let me go!" she yelled out. Dean tugged on Libby, trying to get her out of Lucifer's grasp, but his grip was too tight. Lucifer yanked Libby's arm towards him, holding her by the shoulders.

"Don't think that this doesn't mean I don't love you, honey. I just think you need a timeout. Oh, and Sammy says hello," he told her before turning and shoving her into the hole in the wall. Libby let out a scream as she was sucked in.

"Chdr bvtmon tabges babalon." The hole closed and Lucifer removed the Horsemen's rings from the wall, turning back to Dean.

"Your precious Libby is gone. Where's your mighty weapon now?" He took a step closer to Dean. "I told you... this would always happen in Detroit. "