I re-watched this episode a little while ago, and this popped into my head. Major spoiler's for 5.18 of Supernatural, and minor spoilers for Buffy. The biggest canon change to Buffy is that season 7 started in 2005, rather than 2003.
Disclaimer: Supernatural and Buffy belong to their respective people. I own nothing but the ideas I used to write this story. I did use some dialogue from the series, so if it sounds familiar, that's why. I hope you enjoy it.
Sam stared at Bobby. “What do you mean Adam’s gone?” he demanded.
“Would you like me to say it in Spanish?” Bobby scoffed.
“He’s just gone? What the Hell, Bobby!” Sam shouted, gesturing at the couch where the third Winchester brother had been sleeping fifteen minutes ago.
“Watch your tone, boy! He was right in front of me, then he disappeared into thin air!” Bobby growled.
There was a flap of wings and Castiel appeared in the book-strewn living room with a flutter of loose paper. Dean was hanging unconsciously from his shoulder, blood flowing down his face. “Angels took him,” Castiel said, walking to the couch and throwing Dean onto it.
“What happened to him?” Sam asked, staring at Dean’s battered form.
“I did,” Castiel said in a flat voice.
“What do you mean, the angels took him. You branded his ribs, right?” Bobby asked.
“Adam must’ve tipped them,” Castiel replied. Suddenly the angel stood stock still and took a deep breath and tilted his head to the side.
“What is it now?” Sam asked.
“I was wrong. The air has the taint of magic. Your brother was taken by a witch,” Castiel corrected.
Buffy opened her eyes and stared into the face of her long time friend. “Did we get him?” she asked.
“I think so. Check the couch,” Willow answered, squeezing Buffy’s hands before standing. “Whatever Adam got himself into, we’re now in it. We need to be careful.”
Buffy nodded her head and glanced around the room. “I just hope it worked.”
“Don’t stay up here, then. Go and see him. I’ll clean up here. Go!” Willow insisted, giving Buffy a slight push.
Buffy didn’t need any more encouragement and walked downstairs to find her brother and sister in a fight.
“Where the hell am I?” Adam insisted.
“Who the hell are you?” Dawn shouted back.
“Dawn, you know who I am!” Adam shouted.
“I know that my brother was killed a year ago! I had to identify the body. Now, who are you?” Dawn shouted back.
“Guys?” Buffy said, trying to get their attention.
“I was brought back!” Adam shouted.
“Willow’s not doing that anymore, and she’s the only one powerful enough to do it!” Dawn insisted.
“Guys?” Buffy tried again, a little louder.
“What?” both shouted.
“Now I have you attention. Good. Dawn, Adam is back, and alive, and his normal self, trust me,” Buffy reassured.
“How are you so sure?” Dawn asked.
“Willow called me early last week, remember?” Buffy asked. Dawn nodded. “She told me that there were signs that someone was being returned to finish something. She didn’t tell me who or what they had to do, but she called me yesterday and told me that they were back. Yesterday afternoon, Willow and I found out it was Adam and brought him here.”
“Where is here?” Adam demanded.
“Scotland,” Buffy replied.
“How you feeling?” Sam asked, leaning against the wall in Bobby’s panic room.
Dean sat up wiping the sleep out of his eyes with the hand not cuffed to the bed frame. Being knocked out by an angel felt a lot like getting hit by a cement truck, Dean noted. “Word to the wise: Don’t piss off the nerd angels. How’s it going?”
“Gone where?” Dean demanded.
“That’s what we’re working on. Cas thought it was angels until he noticed that there was magic in the air. Now he thinks it was a witch,” Sam sighed.
“A witch?” Dean repeated. He shook his head and chuckled humorlessly. “This just keeps getting better and better.”
“Yeah, you could say that,” Sam agreed. “Didn’t you once date a girl who was friends with a witch?”
Dean stared at Sam in surprise. “Since when did you keep track of the girls I’ve been with?”
“Since it might help us find our brother before he says yes. We don’t know anything about this witch, or why they would want Adam. What’s the girl’s name?” Sam asked.
“Buffy. Buffy Summers,” Dean sighed.
“Okay, let’s go through this one more time to make sure that I’ve got everything. You’re the vessel of the archangel Michael, who is going to use your body to kill the devil. In exchange you’re going to see Mom again. Did I get everything?” Buffy asked. She stopped pacing the room and glared at Adam.
“You got the first part,” Adam agreed.
“What’s the second part?” Buffy insisted.
“My older brothers,” Adam started.
“Wait, wait, wait! Older brothers!” Buffy interrupted. “We don’t have any brothers but you!”
“That’s right, but they’re my brothers through my father, and he’s the indirect reason that I’m in this mess. I’m a part of the bloodline,” Adam explained.
Buffy sat down and glanced at Willow, who was sitting in the chair next to hers. “What are your older brothers called?” Buffy asked after a few minutes.
“Sam and Dean. From what I understand, Dean is Michael’s true vessel, and Sam is Lucifer’s. Since Dean won’t say agree to kill the devil, it’s up to me,” Adam continued.
“Sam and Dean Winchester?” Buffy asked, thinking back a few years, the face of a ruggedly handsome man with intense green eyes coming to mind.
“Yeah. My dad had two sons when he met mom and had me,” Adam confirmed.
“Let me guess the rest. The angels brought you back to fight this war, which Sam and Dean are trying to do without angelic assistance. The angels know you’re out, and are looking for you so you can commit to your part of the deal. Sam and Dean didn’t let you go though with it, so you got out from under their watchful eye and you’re still planning on agreeing so you can see Mom,” Dawn summed up.
“That’s about it,” Adam agreed.
“Except for one thing,” Buffy corrected. “I’m not going to let you do it either.”
Sam re-entered the panic room and leaned against the wall nearest to the head of Dean’s tiny mattress. “None of the numbers you gave me worked. They were all disconnected.”
“That’s not to surprising. Those were a few years old, and from before Sunnydale became a lake,” Dean commented.
“Why didn’t you say anything then?” Sam asked.
“Would you have believed me?” Dean asked in response.
Sam sighed. “I donno. Right now, all we can do is hope that whoever has Adam will keep him from saying yes.”
Sam shook his head before looking down at Dean. The handcuffed arm was above his head, the other rested on his stomach. He had his eyes closed and was taking deep breaths. “Have you asked Cas to try and find Buffy?”
There was a beat while Sam scrunched his face in thought. “No, I don’t think I did.”
“Maybe he can find her or the witch who took him,” Dean muttered.
Adam looked around. He was back in the park, sitting on the bench.
“You missed your second rendezvous, you know. This is beginning to be a bad habit of yours,” a voice commented.
“This one wasn’t my fault either,” Adam muttered, staring at his feet.
“I still can’t quite find you. Are you still with Sam and Dean?” Zachariah asked.
“Where are you then?” the angel demanded.
“I’m with my sisters,” Adam answered.
“You don’t have sisters,” Zachariah insisted.
“Yes, I do,” Adam corrected, looking up at the angel.
“Who are they?” he demanded. When Adam answered, Zachariah paled. “Why didn’t you mention this before?”
Adam blinked. “You’re an angel, I assumed you knew.”
Zachariah took a deep breath. “Where are you?” he demanded.
Before Adam could answer, another voice spoke. “You will leave my brother alone, Zachariah,” Buffy ordered, crossing her arms and glaring at the angel.
“I think I found her,” Castiel announced.
Sam sighed and leaned back on the couch he was sitting on. “Where is she?” he asked, rubbing his forehead.
“Scotland was the closest that I could get,” Castiel replied. “You are certain that Dean called her Buffy Summers?”
“Yeah. Why?” Sam asked.
“Buffy Summers was once at rest in Heaven. She was dragged out of there without her consent. She is known as an untouchable now, as are those with her,” Castiel explained.
“What’s so special about her?” Bobby demanded.
“She was one of the few people who were given the option of becoming an angel when she died. She had just finished her transformation when she was forced to fall. Because of this, she still has her Grace, and a good deal of power,” Castiel continued. “She was given the rank of an archangel after she fell, so those who would oppose her couldn’t get in the way of her duties on Earth.”
“Now we really need to find her,” Sam sighed. “If she’s so powerful, we could use her help in any way she would give it.”
“I agree, but how are we going to contact her? The only one we have who can find her is also the only one who can’t talk to her!” Bobby huffed.
“I can contact her, I just can’t manipulate her,” Castiel corrected. “I’ll talk to her. If I can, I’ll bring her here.”
“Thank you, Cas,” Sam said, hoping that this Buffy woman wound be a blessing, rather than a curse. The Winchester luck with women wasn’t too great.
Zachariah stood up and faced Buffy. “You’re not allowed here!”
“See, that’s where you’re wrong. You are the one who’s not allowed here. Adam in under my protection and authority, and you will leave him alone,” Buffy demanded.
“I’m not under your orders!” Zachariah hissed.
“You’re on my turf, you’re under my orders. Leave,” Buffy ordered. The air around her crackled with raw power and the sky darkened. Lightning struck a tree behind her, illuminating her wings.
“You won’t stop me from getting his permission,” Zachariah insisted before he disappeared.
Adam’s eyes flew open.
“What just happened?” he demanded, sitting up on the bed.
“I just saved your ass,” Buffy replied from the doorway of the bedroom.
“I don’t understand,” Adam said, confused.
“You don’t want to be Michael’s vessel. Trust me. You’ve got me, and you’ve got Dawn. Mom is happy where she is, and doesn’t want you to do this,” Buffy said, uncrossing her arms and sitting on the edge of Adam’s bed.
“Do you know what I went through while you and Dawn were gallivanting around the world?” Adam demanded. “Aunt Kate and I were eaten alive! She and Mom were all I had!”
“You know that’s not true! I asked you what you wanted to do. I treated you like I treat Dawn! Dawn wanted to stay with me, and you wanted to continue school and stay in the States! So I left you with Aunt Kate. I checked in on you every Tuesday, and you had my number! This isn’t my fault!” Buffy defended herself.
“It might not be your fault directly, but you didn’t come for me!” Adam shouted.
“What would you have me do, huh?” Buffy asked. “I’m not a full angel. I can’t go to Heaven, I couldn’t bring you back. I thought you were happy. I didn’t want you to go through what I did.”
Adam sighed. “I know. But I’m twenty now. I get to make my own decisions. I want to do this. I want to kill the devil.”
“You’re not going to,” Buffy stated, with a shake of her head. “There’s another way.”
“Then find it. Though the last people who told me that have been working on another way for the better part of a year with no success,” Adam relented.
“They don’t have what we’ve got,” Buffy reassured him.
“What’s that?” Adam demanded.
“A witch with connections, a part angel with a very high rank, and the Key. Dawn’s got more power in her pinky than Zach has in his whole body,” Buffy answered.
“You got everything you need?” Sam asked.
“I have everything that I can get to be prepared,” Castiel said.
“You’re going to do this locater spell when you get to Scotland?” Bobby asked.
“Yes. It should show me on a map where she is, if she’s not using her power to hide,” Castiel answered.
“Good luck, man,” Sam said, patting Castiel on the back.
“Thanks. I believe I’ll need it.” Castiel took a deep breath, then disappeared.
“Buffy, where did you say Adam was?” Xander asked, walking into the library where the upper echelon of the Scoobies were working.
“I left him in his room. Kathy’s keeping an eye on him,” Buffy answered, absently turning the pages in the book she was attempting to read.
“I was afraid you would say that,” Xander said. “Kathy was found in the hall outside of his room with a bloody nose and a mild concussion. He’s gone.”
Buffy froze. “What did you say?” she demanded, raising her head to glare at Xander.
“Adam is not in his room, and it looks like a bomb went off. He either trashed his room and walked away in a huff, or he was taken. With the state Kathy’s in, I’m going with the latter,” Xander said. “He’s gone.”
“He’s gone,” Castiel said.
“Who?” Sam asked. “You haven’t left yet.”
“Adam has been taken from the witch,” Castiel clarified. “The angels now have him.”
“Fuck,” Sam whispered.
“We need to get him back,” Bobby stated.
“Yeah, and we’re going to need help,” Sam agreed.
Adam looked around the room. It was tastefully decorated with a big painting of Michael on the wall. Beer and hamburgers sat on the table. He took one of each and sat down at the end of the table. He took one bite and moaned.
“I see you and your brother share the same refined palate.”
Adam looked up and saw Zachariah sitting on the edge of the table a few feet away. He swallowed and took a sip of beer. “So, are we ready?” he asked.
“Ready?” Zachariah repeated.
“Yeah. Ya know, for Michael?” Adam asked, taking another bite.
“Right! I’ve got bad news for you. We’ve been having trouble and have to cut our assets,” Zachariah said in an upbeat tone.
Adam dropped his burger. “Excuse me?”
“You’re a great kid, and all, but you’re not what we’re looking for. You’re more like. . . bait,” Zachariah said, using the pause to infuriate Adam.
“You told me I’m supposed to kill the devil!” Adam insisted.
“No, you’re not. But you are the bastard half-brother of the guy we need to kill the devil. That’s not too bad, is it? Zachariah laughed.
Adam shook his head. He should’ve trusted his sister. “You lied.”
“Not exactly. We just omitted certain things to manipulate you,” Zachariah corrected.
“You son of a bitch!” Adam shouted.
Zachariah laughed again. “You don’t understand, kid. The Winchesters have one blind spot. Family. They’re going to put aside their differences and come to get you, which puts Dean right where we want him: this room. Right here. This is the night he says yes, Michael’s seen it, and it’s all due to you. And me, but who’s keeping score?”
“I’m not going to let you do this,” Adam insisted, standing up.
“You don’t have a choice. No one else is coming for you,” Zachariah informed him. “Besides, you still get your severance. You get to see your mom again.”
“How do I know I can believe you?” Adam demanded.
“You don’t,” Zachariah answered with a shrug. “Now I don’t want to hear you talking anymore.” he flicked a wrist at the teen and Adam began to cough up blood. “That’s better!”
“Fuck!” Buffy yelled. She stormed back to the library. “It was Zachariah! He took Adam. I’m getting him back! Willow, Locater spell, please!”
“On it!” Willow said, spreading out a map of the world. She held out her hand and Buffy placed some hairs into it. Willow began muttering and a light appeared in the United States. Xander handed her another map and the next light appeared in California.
“I know where he is,” Buffy said, and disappeared with a flap of wings, startling Willow, Xander, and Dawn.
Sam sat in front of Dean. “Cas had news.”
“And?” Dean growled, still lying on his back.
“The angels now have him.”
“Where?” Dean demanded, sitting up.
“The room where they took you. Cas did some recon after he felt them move him,” Sam answered.
“Yeah, the place is crawling with angels. It’s almost suicidal to try to get him,” Sam said.
“So, nothing out of the ordinary. What happened with Buffy?” Dean asked.
“Didn’t get that far, figured that Adam was a higher priority,” Sam admitted.
“Right. So, what’s your plan?” Dean asked, leaning against the wall.
“To start with, I’m bringing you with me,” Sam said, reaching for Dean’s still cuffed hand.
“What?” Dean demanded.
“Yeah. There’s too many of them, and you’re the only one I’d trust, other than Bobby, at my back,” Sam said, releasing the cuff and letting it fall to the floor.
“I don’t understand,” Dean admitted. “Isn’t this a bad plan?”
“Well, two out of three say yes, but I’m not convinced,” Sam confessed.
“They’re right. This is more than likely a trap to get me to say ‘yes’ and even if it isn’t, I’m going to say ‘yes’ anyway,” Dean said, rubbing his wrist.
“I don’t think so,” Sam denied.
“I’ve let you rot in here, and you’re bringing me into the fire?” Dean asked.
“When the time comes, you’re going to make the right call. You’re my big brother,” Sam said, as if that explained everything.
“Where are we?” Dean demanded.
“Van Nuys, California,” Castiel answered.
“Really? I thought the room was in some spiffy mansion, not an abandoned factory,” Dean muttered.
“Tell me again why you can’t just go in and grab him,” Sam asked.
“There are at least five angels in there, and I’m not as quick as I once was,” Castiel answered. The three stopped in front of a door. “You two get the boy, I’ll get rid of the angels. This is our only chance.”
“You’re going to take on five angels by yourself? Isn’t that risky?” Dean asked.
“Perhaps, but I don’t have the same faith in you that Sam seems to,” Castiel’s voice was cold. He took a knife out of his pocket and handed it to Sam. He reluctantly carved the angel banishing sigil into Castiel’s chest and sent him into the warehouse.
They waited until they heard a zap, followed by screams. They quietly opened the door and cautiously entered the warehouse. Dean saw a small office in the middle of the floor and ran to it. He opened the door and carefully went inside.
Adam was slumped on the floor, blood slowly trickling out of the corner of his mouth. “Adam, what did he do to you?” Dean whispered. He rushed to the teen, ignoring the door closing in his rush to get to his younger brother.
“You came for me,” Adam whispered, silently wondering where Buffy was.
“You’re family,” Dean shrugged, as if that explained everything.
Adam could picture Buffy responding in the same way.“This is a trap,” he tried to warn him.
“I know. But I’m not going to leave you here,” Dean answered, pulling Adam into a standing position, wrapping his arm around Adam’s waist and pulling Adam’s arm over his shoulder.
“Did you really think it would be that easy?” Zachariah scoffed, appearing behind Dean as he turned around.
“Did you?” Dean responded, seeing Sam behind the angel.
Zachariah batted Sam away, and Sam was thrown into the wall. Dean followed Sam’s progress, panic in his eyes. “You know what I’ve learned from this whole thing? Patience.” He flicked his hand at Adam and the teen began to cough up blood again.
“Adam?” Dean struggled to hold up the teen, who was curling into himself. He gave up and placed his brother on the floor by his feet. “Let him go, you son of a bitch!”
“I mean, I thought I was downsized for sure, you know. And a firing for us is pretty much literal, but I should’ve had faith in Michael. It’s all coming together like he said it would. You, me, your dying brothers. . .” Zachariah trailed off, flicking a hand at Sam, who began to cough and spit up blood.
“And where do I fit in?” a new voice asked.
All four men turned to face the newcomer. “Buffy,” Adam coughed.
“I thought I told you that he was mine, and that you were to stay away from him?” Buffy asked in a thoughtful tone. She walked over to Zachariah and tilted her head.
“You’re not allowed to be here,” Zachariah said gleefully. “Michael’s going to squash you like a bug when he comes down.”
“No, he’s not. Not today, anyway,” Buffy denied. “Michael’s not coming today.”
“One way or another, he is, and there’s nothing you can do about it!” Zachariah shouted.
“Did you forget who you’re messing with? Adam’s got allies in high places,” Buffy said.
“Did you forget who you’re talking to?” Zachariah hissed.
“I’m talking to the angel who took someone under my protection. You forgot that while I’m here, I’ve been given the rank of Archangel, as in Michael’s equal,” Buffy answered. The lights flickered throwing her wings in shadow on the walls behind her. “Find someone else to house Michael. There’s more than one way to fight an apocalypse, and I know that from experience.”
Buffy flicked her wrist at Adam. He stopped coughing and regained his color, but stayed down. Dean bent down and picked up the blade that Sam dropped. He hefted it in his hand, and made a decision. Zachariah’s back was to Dean, and he took that advantage. He thrust the blade into Zachariah’s heart and twisted the knife before yanking it out.
There was a bright flash of light and both Dean and Zachariah were thrown across the room, landing against opposite walls. Black wings extended on either side of him. Buffy ignored the body, walking around the table to kneel in front of Adam. “How are you feeling?” she asked, running her fingers through his hair.
“Peachy,” he groaned.
Dean stood silently as he watched Buffy interact with his brother. He hadn’t seen her for five years, after breaking up with her when he left to find his father. They had talked on and off until Sunnydale became a lake four years ago. He had had other women, but none compared to her. “Buffy?” he whispered.
She looked up, truly seeing Dean for the first time. “Dean,” she said, before returning her attention to Adam. “Is the bleeding all he did to you?” Adam nodded. “Well then, let’s get out of here.We don’t want to gain anymore attention than we already have.”
Dean nodded and rushed to Sam, who Buffy had forgotten about. She flicked her wrist at him and healed him like she had healed Adam. The four of them left the room, Buffy and Adam following Sam and Dean.
Dean turned to face Buffy when the four of them were outside and back in the sun. “Will you stay a bit?” he asked, almost shyly.
Buffy smiled at him. “Sure, but I can’t stay too long. Dawn will worry.”
Dean smiled softly and held open the back door of the Impala, allowing Buffy and Adam to slide in. With Sam in the front, Dean climbed into the driver’s seat and headed back to Bobby’s.