"What do you mean, you can't get us out?" Dean was still shaking with adrenaline left over from the epic battle against the Manticore. He had been forced to call on Castiel for help. He would have been very dead otherwise.
"It is the power of the Manticore," Cas said. "Creatures as old as the Manticore are dangerous even to the more powerful angels… and I do not have much strength left."
"We'll find a way out," Dean said reassuringly. They were several hundred feet underground in the Manticore's lair, and the entrance to the cave was had been blocked by a rockslide. Not reassuring at all.
"I do not see how-" Castiel started to say, but he stopped and fell to his knees.
"Cas?" Dean quickly knelt beside his friend. Cas was pale. When Dean laid a hand on his forehead, it felt clammy. He gently helped Cas lie down, bunched up his coat and laid it carefully beneath the angel's head. "What's happening to you?"
"It's… poison," Cas answered weakly. "From the Manticore. It's in the air of this cave. If Sam had not given you the antidote, you would have been dead from the moment you set foot here."
"Shit," Dean said. He tried not to panic yet, but Cas really wasn't looking well. "Isn't there anything you can do?"
"If there was anything, I would have done it," Cas said. "The poison will kill me."
"No," said Dean. "No way in hell. I'm not letting you go anywhere, Cas." He glared into the angel's deep blue eyes, looked for any reassurance.
"Dean," Cas said softly. He smiled at his best friend. "You have always been so loyal to me."
"You're not going anywhere, Cas," Dean said frantically, desperately searching his mind for anything he could do. He was blinking tears out of his eyes, and he didn't even care.
Castiel shook his head, as much as he was able to move. "Let me go, Dean," he said. "I have known for a long time that my destruction would come. It is better than I hoped; you are here to comfort me."
"No. No way, Cas. Not happening. You are not leaving," Dean sobbed. There had to be a another way! There was one. Something that Dean had never thought he would do. "Cas." Dean gripped the angel's cold hand. "There is a way out of here for you," he said firmly. "I'm going to give you my consent, Cas. I can't see you die."
"Dean…" Castiel stared up at him with a strange expression on his face.
"Do it, Cas," Dean said, "Yes! I give you my consent! I'm willing to be your vessel. I trust you, okay? Just don't die here, when I'm giving you another option, dammit!"
Suddenly Castiel's hand was crushing his. The angel's eyes were literally glowing blue, lighting the cavern with more than just torchlight. Then there was a very bright flash of white light.
When Dean regained consciousness, he was sitting cross-legged on the rocky dirt floor of the cavern. Castiel's vessel was a few feet away, but was obviously nothing more than a corpse. :Cas?: he said, or rather tried to. He didn't have any control over his mouth, so it came out as nothing more than a thought.
"Here, Dean," Castiel said aloud, and it was strange for Dean to hear his own name coming out of his mouth and sounding like someone else, like a mixture of him and Cas. He slowly became aware of Castiel's presence within him. His mind processed it as a network of white light that was spread over his body. Tenuous strands of energy that gave off a barely audible hum. It seemed more fragile than he had thought it would be. He could also sense Castiel's immediate thoughts and emotions; right now there was mostly concern for Dean, and Castiel's gratefulness that Dean would let him share his body.
:Well, I couldn't just sit there are let you die!: Dean said. :And this is a one-time deal, you understand?:
"Of course," Castiel answered, and Dean was still surprised by his, Castiel's, their voice. "If we manage to bring my vessel to the surface and administer the antidote, I should be able to revive him."
:So how are we going to get out of here?: asked Dean. He tried to look around the cavern, but his eyes wouldn't follow his directions. Dean had the feeling that he could fight, tearing at the white light that had settled in them, and it would work. But he had a feeling it would hurt Cas, so he waited for the angel to direct his eyes in a careful sweep of the cavern.
"Thank you for not fighting me," Cas said slowly. "It is very considerate."
:I thought vessels weren't able to take control,: Dean thought at Cas.
"Normally it does not happen. It is a sign of the weakness of my Grace." Their voice echoed in the cavern. It was large, at least a couple hundred feet wide, and dimly lit by torches lining the walls.
:Over in that corner! Is that a doorway?: Castiel brought Dean's eyes into focus at the dark edge of the cavern. "It looks like it," he said hopefully. They stood up and walked toward it, Dean feeling distinctly odd about the way Castiel moved him. His posture hadn't been that kind of straight-up-and-down since, well, it probably never had been. Too easy to get knocked over.
They opened the ancient wooden door. A set of stairs spiraled upward into darkness, but there was also the faint scent of fresh air. :This must be it,: Dean said. "Yes," Castiel agreed. He returned to the center of the cavern to pick up his vessel. :Why can't I have super-strength?: Dean grumbled as Castiel lifted the body effortlessly. "It is not worth being possessed," Cas said seriously. :You're right. It would just… be nice. To have the kind of strength that the enemies always do. I could protect people. I wouldn't have needed to call you here, and almost get you killed.:
"You do not need super-strength, Dean. What happened here is not your fault, and we are both alive." Cas flooded him with feelings of gratitude again. It was like being hit with a tidal wave.
It did not take long to reach the reach the surface. Dean figured out how to relax and let the angel take control while he sat back and observed, with a tiny bit of jealousy. Cas wasn't even winded after climbing hundreds of stairs while carrying a dead body.
The staircase ended with a trapdoor, which led into a gardening shed in a park not too far from where Dean had parked the Impala. People gave them plenty of odd looks on the way there, but Cas completely ignored them, as if carrying a dead body around was the most normal thing in the world. Dean would have laughed out loud if he could. Instead, he settled for mental chuckling and tucked away the memory for when he needed something to laugh about. This one was going to last.
"The antidote?" Castiel asked when they got to the car. :Glove compartment,: Dean replied. :Keys are in my left pocket.:
Cas found the vial of liquid and arranged his vessel in the passenger seat. Dean winced; it was like staring into the face of a dead Castiel, even if he knew that was not the angel's true form. It scared him, just a little. What had Cas said in the cavern? He had known that his destruction would come… "Dean," Castiel said, "I merely meant that I see the world as you mortals do. Nothing lasts forever. There is no greater-than-usual reason to see death in my future."
:I just wish there was no reason at all. You deserve better.:
"As do you. We both know it is unlikely to happen." There was nothing that Dean could say to that, so he stayed silent and watched as Castiel used his angel powers to get his dead vessel to swallow the antidote. More angel mojo brought the vessel's systems back to life. His heart pumped blood and his lungs drew in air. The venom reacted to the antidote, and the effects of the poison drained away. Finally, blue eyes opened mechanically. "I am ready," Cas said.
:Cas?:
"Yes, Dean?"
:I'm… glad I could trust you with this.:
"I am also glad, Dean." Castiel put a hand on his vessel's forehead, and there was another bright flash of light.
Dean woke up in the driver's seat of the Impala. Castiel was watching him from the passenger's side. Dean found that he could move his body. It was a relief to be able to focus his own eyes, slouch in his own way. But he hadn't minded Castiel's presence that much. The super-strength had been pretty great… and when Castiel was inhabiting him, Dean had known that there was absolutely no chance of his teleporting away without saying a word. But Cas wouldn't do that anyway, these days, and he deserved Dean's trust. They had certainly proven that, too.
Dean grinned, punched Cas in the arm playfully. "Well, that was exciting," said. Cas didn't return his punch, but he grinned back, and it was more than enough. That was all the discussion the two of them needed. Dean started the car and they drove on to the next adventure.