A/N: Because I forgot to mention this in the note to the previous chapter: Major thanks to my fabulous beta Ansostuff! And thanks, too, to AuntMo for inadvertently suggesting this chapter title. The song Dean gets stuck in his head is "Set Me as a Seal" by René Clausen, and the National Lutheran Choir's performance is available on YouTube; it's a setting of Song of Songs 8:6-7, whence also the title of this story. I'm relying on the timeline by hells_half_acre (on LJ) for the setting of the memory. (Side note: the word love in these verses, Hebrew 'ahabah, is translated as agape in the Septuagint. So it really is appropriate for this context.)

Chapter 2
Look Out (Here Comes Tomorrow)

Dean's stomach growled as they left the VIP quarters and nodded to Cas. "C'mon, Sammy. It's..." Taco Tuesday, he nearly said before remembering that it might not be wise to bring that up again. "After one," he said instead, "and Teal'c says there's somethin' really good in the mess hall today."

Sam looked a little queasy still, but he shrugged. "Have you eaten yet, Cas?"

Cas looked surprised. "No. I was waiting for you."

Dean shook his head in disapproval. "Can't skip meals now, Cas. You have to eat. We don't want you getting sick again."

Cas looked like he was about to object that he had only been injured last time, not ill, but his own stomach growled loudly and ended the discussion.

Carter was deep in conversation with Daniel and Teal'c when they got to the mess hall and looked a little guilty when she saw them coming toward the table with their trays. (Well, Dean and Cas had trays. Sam had a bowl of soup in one hand and a bowl of blue Jell-O in the other.) "I'm so sorry, Castiel," she said. "I completely lost track of time."

"It's okay," Cas replied, the human idiom still sounding odd coming from him. "Your presence was not required. We were in no danger."

"Still, I didn't mean to leave you standing out in that hall all by yourself for so long. It must have been boring."

"Castiel is incapable of becoming bored," said Gabriel, strolling up to the table with his own tray of tacos and with Bobby Singer in tow. "I wouldn't say he's patient, exactly, just easily entertained."

"Explains why he puts up with these two idjits," Bobby rumbled, ignoring Cas' slightly offended frown. "How'd it go, boys?"

"It went," said Sam vaguely. "We weren't expecting you till later."

"Gabriel drove."

Sam and Dean exchanged a look that said I don't want to know and settled in for a stretch of tolerable food and much better conversation.

Dean had his game face firmly in place by the end of lunch, and at a break in the conversation he clapped his hands once to change the subject back to the task at hand. "So! That's done. Now what?"

Sam sighed. "Now I guess we try to find enough demons for me to kill and drain."

"Uh, actually..." Carter interrupted. When they looked at her, she continued, "Dr. Beckett was able to isolate the protein we think is responsible for the 'demon blood' effect, and it doesn't seem to have a kill switch like the Croatoan virus does. We could probably synthesize enough for you not to have to actually drink any blood, even include all the right minerals in the solution. Dr. Lam won't be happy about it, but... I thought I should offer."

Dean blinked. "So, what, he'd inject it like insulin?"

"Pretty much, yeah."

"Would that work, Cas?" Sam asked, sounding more hopeful than he probably meant to.

Cas frowned at Gabriel, who shrugged. "I don't know," said Cas. "I suppose it's worth a try."

"Dean?"

Dean sighed. "You know I don't want you anywhere near that stuff, Sam. But if that's what it takes, then yeah, I'd rather you shoot up the protein."

"If I never taste blood again, it'll be too soon," Sam confessed quietly.

Carter gave him an empathetic grimace and turned to Cas. "How much will he need, Castiel?"

Cas shrugged. "Ordinarily, he would need at least four gallons of blood, but the presence of the symbiote should sustain him with less. I don't know how much protein that works out to."

Carter nodded. "We got a blood sample from Brady. It won't be hard to replicate."

"That's it, then," Sam agreed. "Let's do it that way."

Carter nodded again and started to leave, then stopped and turned back. "You know... Lucifer's hanging out in the Badlands right now. We could probably get the protein synthesized before he moves again."

Sam shook his head. "No. He knows we know he'll be in Detroit. There haven't been enough omens in the Dakotas to justify our looking for him there. If there's any chance at all of keeping you guys off his radar long enough for me to jump..."

"Yeah. Okay. I'll... go talk to Dr. Lee." And she left.

Although he was one of the last civilian scientists left on the base, Dr. Bill Lee didn't have any objections and didn't foresee any problem with synthesizing the amount of protein required in the time available. Dr. Carolyn Lam, on the other hand, had multiple objections and argued them strenuously:

"There is no way a human can possibly ingest that much blood in such a short amount of time. And even if there were, the body can't process that much protein—I mean, look at these saturation levels compared to Ronon Dex's Wraith enzyme levels after he was captured in 2008, and he barely survived the withdrawal. To say nothing of how it will affect Salim! You cannot expect me..."

"Doctor," Dishon finally interrupted. "What dosage of the protein would you consider an overdose?"

"It shouldn't be in his system in the first place! Why are we talking about giving him more?"

"Doctor." This time Cas added his voice to Dishon's.

Lam took a deep angry breath and let it out again. "You do realize what you're asking."

Sam nodded unhappily.

"I'll take the blame," Carter said quietly. "It was my idea to synthesize it."

Lam relented and came up with a figure, and Cas told Lee to make one microgram less than that.

Lee did some quick mental math. "That will just about fill four syringes."

Sam groaned. "I am gonna look like a junkie."

"Well, actually..."

"Bill," Gabriel interrupted. "Just do it."

Lee nodded and scurried out of the infirmary.

The humans had ample time for a long nap that afternoon, which Bobby, at least, needed; it was a nineteen-hour drive from Cheyenne Mountain to Detroit if they went straight through, longer if they stopped for meals, and Sam and Bobby argued that it was best to just get there rather than trying to find a motel on the road. Dean wanted to go anywhere but Detroit, but he understood and agreed. There was no point in delaying the inevitable.

It was just that Sam was planning to end his own nightmares by making one of Dean's very worst ones come true.

Dean knew he wouldn't be able to sleep, but Dishon insisted that he lie down for a while anyway. If the worst should happen, you will need your strength, Dishon noted.

So Dean sighed and did as his symbiote asked. And he tried to come up with something by Metallica or Led Zeppelin to hum that would help him relax. But what he kept coming back to was a song he'd heard the previous winter, when he and Sam had hung up their spurs for a while and holed up at Bobby's while Dean recovered—physically, at least—from the last beating he'd taken from Alastair. There'd been some national choir giving a concert at the Lutheran church on Valentine's Day, and for once Dean let Sam drag him out of the house to go to it, even though he expected to be thoroughly bored, because there was nothing on TV, they'd seen everything that was in the movie theater that was worth watching, and neither of them felt like going to a bar. And he had been bored, mostly, though it wasn't all bad music, and it had been time with his brother that he hadn't had in quite a while. This one song, though... this one had stuck with him, and he'd recalled it that morning when he was sharing his brain with Sam:

Set me as a seal upon your heart,
As a seal upon your arm,
For love is strong as death...
Many waters cannot quench love,
Neither can the floods drown it,
Neither can the floods drown it...

Part of Dean, in the deepest depth of his heart of hearts, still wanted to believe that God cared in spite of everything they'd been through, in spite of His refusal to intervene. And once in a while that part wriggled past all of his defenses and got off a prayer before he could stifle it. Like now. He found himself praying that the song was true, that his love for Sam and Sam's love for him would be the seal that bound Lucifer in Hell once more as well as the lifeline that would bring Sam back to him in spite of everything.

He had nothing else left to give except his life, and he knew for a fact that Sam didn't want him doing that again.

Lee handed over the syringes just in time for Maj. Gen. Hank Landry to ask Team Free Will to come to a final briefing with Atlantis before they left. Atlantis, they learned, had sent two ZPMs to Earth to allow the Apollo and the Daedalus to join the Odyssey in evacuating most of the key non-military IOA and SGC personnel—along with several irreplaceable pieces of technology and database backups, one irreplaceable Jeannie Miller and her family, and one highly irreplaceable Master Bra'tac of the Jaffa—to the Pegasus Galaxy, since not even Gabriel was clear on how the whole prophecy about the stars was supposed to play out. The Ancient power sources enabled the Asgard hyperdrives to get the Earth ships to Atlantis in four days rather than three weeks. China had sent the newly repaired Sun Tzu to guard the Alpha Site, whence Lt. Gen. Jack O'Neill intended to evacuate most of Earth's leaders if necessary, and Russia had sent its only ship to the Tok'ra homeworld. Only the Hammond remained in orbit around Earth, waiting to return O'Neill to Washington and to allow Carter to track the Winchesters as they made their move.

Dean didn't pay much attention to most of what was said during the briefing, being too busy wishing that he could drag Sammy to Atlantis now and let the angels and demons have Earth to themselves. But he did perk up when Dr. Carson Beckett announced that he and the Wraith known as Todd had finally finished their vaccine for the Croatoan virus.

"Ironically, it was Dean's blood work that held the final piece of the puzzle," Beckett explained. "We still don't know what that unusual antigen of his does, but we combined it with the Wraith serum and the Prior plague vaccine, and it seems to have done the trick. Of course, computer simulations can tell us only so much, but it looks like we've cracked it. I've sent the formula in the data burst."

"Awesome," grinned Dean.

"We'll hold onto it," O'Neill replied. "Hopefully we won't need it, but it won't hurt to have it on hand. Thank you, Doctor."

Beckett nodded and sat back in his chair.

And finally the moment they'd all been dreading arrived. O'Neill turned to Team Free Will and said, "Now, I understand you guys have figured out a way to end this once and for all, or at least for the rest of this century. Would you mind filling us in?"

Sam rubbed his hands on his thighs nervously and cleared his throat. It was one thing explaining his buckets-of-crazy plan to Dean, Dishon, and Cas at Bobby's kitchen table; explaining it to this crowd was something else, and Dean didn't blame him for being nervous. But they'd all agreed that Sam was in the driver's seat, all the way, which meant he was also in the hot seat at the moment.

"This is as much Salim's plan as it is mine," Sam began slowly. "It was my idea, but he figured out how to make it work. He wouldn't be going along with it if he hadn't. So I've asked him to explain it to you."

His head bobbed, and his spine straightened as Salim took over. "My brother Dishon has likened this plan to using the weapon platform on Dakara, a dangerous plan with high risk of failure and cataclysmic consequences, only to be undertaken as a last resort. He is not wrong. But as in the final battle with the Replicators, we have no remaining alternative.

"We have now secured the components necessary to open Lucifer's cage, and Dean and Dishon alone know the incantation required. We have also secured the ingredients necessary to prepare Sam for his role. There is no way of telling how they will affect me, so once we are in position, I shall hibernate until I am needed.

"The plan, simply stated, is this. Tomorrow night Lucifer will be in Detroit. He expects Sam to meet him there and agree to be his vessel. What he does not expect is that Dean will accompany Sam to the meeting. Dean will then open the cage while Sam wrests back control from Lucifer long enough to jump through the opening. Lucifer will not need his vessel once he has been returned to Hell, so once Sam is free of him, he shall wake me, and together we shall set about finding our way to a hellmouth and make our escape. Hell, it seems, is set in a time dilation field that is faster than Earth time by a ratio of 120:1, so if we have not returned to the surface within twenty Earth months, you may assume we have perished. But under no circumstance is anyone to attempt a rescue."

Dean hadn't been sure whether to expect silence or an explosion, but the silence was deafening until O'Neill leaned forward and said, "You're talking about a suicide mission here."

"We are aware that our return is unlikely," Salim replied calmly. "But it is our only option."

"That's not what bothers me, General—with respect," stated Lt. Col. John Sheppard. "I mean, between you and me alone, we've pulled off, what, dozens of suicide missions?"

O'Neill sighed. "Hate to admit it, but there were a few of 'em I didn't survive. Winchester's not gonna have access to a sarcophagus."

"But the point is we survived more than we should have, so 'suicide mission' officially doesn't mean much to the SGC. What bothers me is this 'wrest back control' part. I'm not exactly an expert on demon possession, but that doesn't sound too likely to me. So what happens if Sam can't make the jump?"

"Then Michael will meet Lucifer on the chosen field," Cas answered, "and they will fight, and the world will end."

Another silence followed, again broken by O'Neill. "I can't authorize this. I can't imagine the Tok'ra High Council going for it, either."

Dishon nudged Dean, who stepped back. "I am sorry, General, but you have both been overruled."

O'Neill frowned. "Who could overrule me and the Tok'ra?"

"Death."

Now the incredulous stares were on him rather than Salim, and he could almost hear Sam's mental What? Dean had hoped with all his might that they wouldn't have to play this card, but since they had to, he was glad Dishon was the one doing it—and that Salim was driving at the time, because Sam would explode.

"Come again?" said O'Neill.

"We could not kill Death nor take his ring by force," Dishon explained. "But he was willing to give us the ring and the incantation on the condition that we return Lucifer to Hell by any means necessary, even at the cost of Sam's life. Seeing no alternative, we agreed. At the time, Dean still held out hope for another option. But we have exhausted every other possibility."

"And before you ask," Gabriel added, "no, no one else is capable of doing this. Lucifer's already got a temporary vessel, even though Nick's falling apart right now. He won't settle for anyone less than Sam."

Dr. Rodney McKay held up a finger. "I thought Armageddon was supposed to take place outside Jerusalem."

Gabriel just shrugged.

Sheppard looked at McKay oddly. "When did you become Mr. Bible Trivia?"

McKay rolled his eyes and didn't answer.

O'Neill sighed. "Have I mentioned lately how much I hate surprises?"

"You are not alone in that," Cas remarked dryly.

"I... I can't authorize this mission. But I can't order you not to do it, either. So... I guess I'll just say... Godspeed."

The Tok'ra bowed their heads in acknowledgment.

"Atlantis, check back with us Friday morning at 0900. If we don't answer... you'll know you're on your own."

"Understood, General," replied Richard Woolsey, the commander of Atlantis. "And Sam, Dean, I too wish you Godspeed on behalf of the humans of the Pegasus Galaxy."

"Thank you, Mr. Woolsey," Dishon returned. "We thank you all for your assistance. And we hope to return to you with good news."

"See that you do," said O'Neill. "Dismissed."

The Gate shut down, and the people remaining in the briefing room filed past Sam and Dean to at least shake hands. A few, like Daniel, wished them luck. Teal'c clasped their forearms in a warrior's handshake, and his "I wish you well" managed to convey more than Dean had ever thought four words could possibly mean.

Carter was the last person to say goodbye to Sam, but he couldn't let her leave without truly thanking her, so when she turned to go, Sam said, "Um, Colonel?"

Carter turned back to him. "Yes?"

"I, um... I... wanted to say thank you. For everything."

She blinked. "Um. You're welcome."

"Just... I don't have all that many memories of her first-hand, but... you remind me a lot of my mom. And..." He trailed off, unsure of how to continue.

She blinked again for a moment, and Sam could see that she was blinking back tears. Then she pulled him into a hug, and he very nearly broke down himself.

"I cannot begin to imagine what you're going through or what's waiting for you down there," she whispered. "And I am so sorry you have to do this. If there were anything I could do..."

"You have, Colonel. You've done so much, I can't even... I don't want to know how much harder it would have been if it had just been me and Dean. Yeah, we'd have Bobby and Cas, and we would have been stuck with Crowley, but Gabriel would have died, and... you've helped. A lot. You all have."

She sniffled and patted his arm. "Hurry back."

He smiled wryly. "We will."

Meanwhile, Dean was taking a head count and noticed that Gabriel was lounging in the doorway to the briefing room. "You comin'?" Dean asked.

"Nope, I'm staying here," Gabriel said. "You don't need me for this anyway, but these people need protection, and we can't let Lucifer get to the Stargate. Between Sam and Salim, he'll know enough to be dangerous."

"Okay. Don't come after us until you're sure it's over."

Gabriel nodded and lowered his voice. "Dean. I wasn't lying in Muncie, when I said I'd seen how it ends. But I suspect now that all I saw was a probable future. Yogi Berra was right; it ain't over till it's over. Do not give up hope, no matter what happens in Detroit. You may be Sam's greatest weakness, but you're his greatest strength as well. I should have realized that a lot sooner."

Dean knew this was probably as close as Gabriel was ever going to come to apologizing for the Mystery Spot. "Thanks, dude. Really. Thanks for everything."

Gabriel nodded again, and Dean left, snagging Sam on his way out the door.

On their way to the parking lot, Bobby insisted both that he drive his own van and that Cas ride in the Impala. Cas looked hurt until Bobby pointed out that the van didn't have a comfortable place for a passenger to sleep, "and you look like you're gonna need sleep, son. You still ain't completely well for a human."

Cas sighed and climbed into the back seat without further argument.

Neither Sam nor Dean said much until they reached the South Platte River, which prompted some Oregon Trail jokes. By that time, Cas was sound asleep and snoring, and somehow that seemed to help both brothers feel that they could address sore points remaining from the briefing without shouting at each other.

"I can't believe..." Sam began, then stopped.

Dean glanced over at him. "What?"

"Death."

Dean sighed. "Like Dishon said, I thought there had to be another way. Some kind of bait, somethin'. I mean, you know I would never..."

Sam looked at his hands a little guiltily. "Yeah. I guess I do." Then he looked over at Dean again. "You were seriously going to try to cheat Death for me?"

Dean shrugged. "Done it before."

Sam chuckled.

"But by then I guess I was the only one who thought we had another out. And after that last talk with Dishon, I didn't think it would matter to you that Death's ring came with strings attached. I didn't... I mean, I didn't expect O'Neill to be okay with this, but I didn't expect to have to pull rank like that, either."

"Well, technically, Dishon was the one who pulled rank."

Dean snorted, accepting the comment for what it was, and they were silent for a few more miles.

"So what is this about no rescue missions? You guys including me in that?"

"Yes. You've got to promise not to try to bring us back."

"No. You can't ask me to sit by and do nothing."

"I'm sorry, Dean, you have to. If there is a safe way out, Salim and I will find it. But once the cage is shut, you can't go poking at it. It's too risky."

"Then what am I supposed to do for the next two years? Twiddle my thumbs? Dishon and I talked—we're not gonna go back to the Tok'ra because I am not gonna be halfway across the galaxy when you get out."

"Then find Lisa. Pray to God she's dumb enough to take you in. And you have barbecues and go to football games. You go live some normal, apple-pie life for a while, Dean. Promise me!"

You know he's right, Dean, Dishon said sadly. We don't have much choice.

Dean sighed. "Okay. I promise."

Sam heaved a sigh of relief and relaxed back into his seat. "Thanks."

The only sound for the next hundred miles was Cas' snoring.

It didn't take them long to find the right spot in Detroit; the temperature suddenly plummeted twenty degrees, and Carter confirmed the coordinates when they called the Hammond. Once they were parked outside the house where Lucifer was hiding, Sam and Salim each said their farewells to Bobby and Cas. Then the blended hunter came back to the Impala, emptied his pockets, and took the syringe cases out of the trunk. His hands shook as he opened the first one.

"Dr. Lam said to inject it in the neck, right?" he asked, struggling to keep his voice level and not looking at Dean.

"Yeah," Dean replied quietly.

"Do you mind not watchin' this?"

Dean started to turn away, but Dishon nudged him and took over for a moment. "Sam, let Salim do it."

Sam blew the air out of his cheeks. "Okay. Thanks, Dishon."

Dishon relinquished control, and Dean walked to the front bumper of the Impala, keeping his back turned as the quiet hiss of the injectors marked a gradual increase in his brother's breathing. By the time the trunk slammed shut, Sam was puffing like he'd just run a four-minute mile.

"G'night, Salim," Dean heard him murmur, and then Sam was stalking up behind him, radiating anger and determination. "All right. Let's go."

And Dean followed him into the lion's den—and came out alone.