"What a peculiar thing you are," Lucifer murmurs, eyes intent on his.
Castiel watches the Morning Star, mentally testing the confines of the holy fire circle. It holds him firmly; he's still an angel, no matter how far he's fallen, but this is of no help to him now.
"What do you want?" he finally asks as the silence stretches on with Lucifer seeming content to just continue observing him.
"I don't suppose you'll remove the sigils hiding Sam Winchester from me?"
"I won't." His response is instant.
"You and I both rebelled, Castiel. Heaven wants you dead almost as much as they want me dead." Lucifer's voice is soft and coaxing. "We're on the same side here, so why not just serve your own best interests and join me?"
"There's a massive flaw in your argument. Joining you would mean wiping out the whole of humanity, and that's the exact opposite of what the Winchesters and I are trying to achieve."
For the first time since this conversation started, Lucifer's mask of cool, condescending curiosity cracks to reveal a dark fury beneath.
"Humans are flawed, broken creatures. They fight and kill amongst themselves, a pile of depraved cockroaches. There is no worth in them," Lucifer growls.
"You speak only of the malevolent humans. What about the good, strong, loyal ones, people like the Winchesters? They are the ones worth saving."
"And look where that path brought you! You're falling and fading, brought low by your love for humanity!" Lucifer is pacing now, long agitated steps back and forth.
"This is merely a test that God has given me," Castiel states.
Lucifer whirls around. "Our Father is long gone, Castiel! He will not return until we play out this long-foretold Apocalypse and wipe the slate clean, and maybe not even then! If He wanted the humans to prevail, He would have given a sign by now and not let events come this far!"
"He has given a sign. Given me a sign. Given the Winchesters a sign." Castiel stares at Lucifer's decaying vessel, remembering the burning intensity of an archangel shredding him into nothingness. "I was slain by Raphael just before the final seal was broken."
Lucifer stills.
"I was revived, whole and intact," Castiel continues, "and the Winchesters were transported onto an airplane from the room where you first emerged. Those were clearly the acts of the Lord, indications that He wishes us to save the humans, to continue opposing the conclusion of the Apocalypse."
Lucifer is unmoving, face turned away. When the Morning Star looks back at him, the anger is gone from his features, replaced by an unidentifiable emotion. "I killed more than a hundred of Carthage's townspeople today. If God truly cared about the humans, he would not have allowed me to do it. You can't possibly still have faith in Him after the many innocent casualties that have been stacking up ever since the first seal was broken."
"I…" Castiel hesitates, thinking back to the spiralling doubt that's consumed him ever since meeting the Winchesters. So much uncertainty about his Father and His plans; his belief in the Lord is not as invulnerable as it used to be.
There is a right and there is a wrong here, and you know it.
"I have faith in humanity," Castiel says quietly, resolve steeling. "I believe in free will. God does not control our every action. You and the other angels made your own choices, to murder innocents to serve your own ends, to bring about a fate that is not set in stone. I managed to see what you and the rest of our brethren are blind to – humans are imperfect, and they make mistakes just like we do, but unlike the angels, people are willing to forgive, willing to change for the better. They are willing to do the right thing. For that alone, they are worthy of salvation."
For long moments, they stand motionless, staring at each other. When Lucifer finally moves, it is to raise a hand and flick it through the air towards Castiel. The angel braces himself to be eradicated, but instead the holy fire circling him extinguishes itself, freeing him.
Startled, Castiel glances down, and jerks backward in surprise as a tendril of grace brushes against his own. He calls a blade to his hand, taking a defensive stance, but between one breath and the next, Lucifer is gone.
He wavers, but decides that this is not the time to debate the Devil's idiosyncrasies, and flies to where he can sense the gathering of hellhounds.
His presence is enough to turn the tide of the battle; Meg flees with the remainder of the pack after he kills one too many of the canines. Afterwards, they search the town. The Reapers are gone and corpses are sprawled around the mass grave with remnants of a half-completed ritual lying abandoned.
Lucifer is nowhere to be found.
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Afraid that the Harvelles are now a target, he engraves the Enochian sigils into their ribs before allowing them to leave, then spends the next few days helping Dean and Sam on a hunt. The brothers know that Lucifer trapped and attempted to recruit him, but Castiel lets them think that he escaped on his own rather than telling them that the Serpent had voluntarily released him without harm. He would like to think that his words had an effect on Lucifer, but he knows better than to be so naïve; the Devil probably had another plan in mind.
He's contemplating the same issue again as he stands on the top of a mountain in Scotland during yet another attempt at finding his Father, when the flutter of wings disrupts the peaceful silence.
He spins around, and somehow isn't surprised to see Lucifer standing behind him. The Morning Star stares out over the side of the mountain at the scenic view beyond, hands tucked in his vessel's jacket pockets, quiet.
Castiel is readying himself for a rapid series of jumps to shake the Devil off when the other angel speaks, "Has Gabriel returned to Heaven since my imprisonment?"
Castiel pauses, and then answers cautiously, "No. The Messenger is still missing from our ranks."
Lucifer nods slowly, something melancholy in his countenance, and disappears.
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Castiel is in the Rocky Mountains the next time the Devil finds him, and he belatedly realises that Lucifer must have tagged him back in Carthage.
"Join me for a meal, won't you, Castiel?" Lucifer places a hand on his shoulder, and it's not a request. The other angel gives him the illusion of choice by waiting for him to nod stiffly before taking them to Wilmington, Delaware.
They eat seafood in a small, out-of-the-way restaurant, Castiel chewing mechanically. Bobby and the Winchesters have introduced him to a wide range of food over the past months, and Castiel judges the meal to be one of the best-tasting ones he's had, but he can barely appreciate the taste because of the presence of his dining companion.
"This is one of Nick's favourite restaurants, you know," Lucifer comments idly when the main courses are cleared and they're waiting for the dessert.
"Nick?"
Lucifer smiles and taps his fingers against his own chest. "This vessel."
"I… see." Though Castiel really doesn't. It begs the question of why Lucifer, who detests humanity so much, would be sentimental enough to eat at a backup vessel's favourite restaurant. He almost voices the question, but the ringing of his cell phone stops him.
Without knowing if it's a good idea, but entirely thrown off by the circumstances, he picks up the call.
"Cas, where are you?" comes Dean's harried voice.
"What's wrong?" Castiel is conscious of Lucifer's gaze on him.
"Sam and I could really use your help with this Wraith we're hunting. We're at – "
"Dean!" he cuts the man off anxiously. "I – I believe I might be being followed by Lucifer. It's not wise for me to go to you right now."
Inventive curses spill down the line. Castiel hastens to assure him that he's well, and that it's better for the angel to stay away from the Winchesters for the time being.
"Fine, you know where home base is. If it comes down to life or death, you fly your feathery butt over to us, you got me? I won't let you get shanked by that bastard!" Dean snaps over the phone, fierce and protective.
Castiel doesn't realise he's smiling until he hangs up and meets Lucifer's eyes; the smile falls off his face as questions well up inside him. Why hasn't Lucifer trailed Castiel back to Sam? Why is Lucifer seeking Castiel out like this? What is Lucifer up to?
"Does Dean really think he can make a difference if I decide to kill you?" Lucifer asks mildly.
"Perhaps not, but he will certainly try his best, and that is all that matters."
Lucifer nods, looking like he at least respects that kind of spirit, and then their coffee tiramisu arrives.
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The situation repeats itself, the fallen angel appearing at his shoulder when Castiel is alone and bringing them around to various places. Nick's body deteriorates with each visit, but Lucifer doesn't show any desire to do anything about it. Castiel had been forced to go to the Winchesters when the brothers found themselves in the middle of a life-threatening hunt, but Lucifer hadn't taken advantage. On the Apocalypse front, everything is oddly quiet, with none of the three remaining Horsemen appearing.
Somewhere around the fifth visit, Castiel comes to the realisation that the Devil is lonely.
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Three months to the day Castiel met the Serpent in Carthage, Lucifer pops into the motel room where Castiel has just banished a ghost haunting the building. They wait together silently, Lucifer gesturing dismissively at the screaming ghost when it reappears. Eventually, the spirit bursts into flames, signalling a successful salt-and-burn by the Winchesters at the cemetery.
Only then does Lucifer speak. "You remind me of Gabriel."
Castiel tilts his head.
"Not a lot, but enough. He liked the humans straight off the bat when Father first created them. Thought that they were interesting, curious creatures. 'They're not like us, brother. They keep changing. Coming up with new inventions all by themselves to better survive,' he used to tell me." The flickering lighting casts shadows on Lucifer's pensive expression. "But even he never thought to question their prophesized doom. He simply thought it was a pity and a waste that these remarkable beings were to be destroyed in the future."
Lucifer is standing in front of Castiel now, looking down at him with ancient eyes. "And yet you, a humble Seraph, think that you can alter the course of destiny, a road that humanity has been travelling down ever since the time of Cain and Abel."
It's not a question, but Castiel gives an answer anyway. "Yes."
The Morning Star smiles softly, and Castiel can see why Lucifer was once known as the brightest one in all of Heaven. "Do you know something, Castiel? Amongst all my brothers who love our Father so purely, I think that your faith and conviction in humans, tempered by doubt and experience, shines the strongest."
Large hands reach to cup Castiel's cheeks, tilting his head up to meet dry lips.
By human standards, it is a chaste kiss, gentle and unhurried. Unseen by mortal eyes, however, Lucifer's tainted grace stretches to meet his own diminished one. Castiel has been cut off from his brethren for so long, devoid of the familiar, welcoming warmth of the Host, so that now even Lucifer's corrupted grace feels like a balm. He lets the Morning Star curl them together, grace to grace, wing to wing, close and intimate.
Lucifer feels starved, an empty void pressed up against him, and Castiel remembers that it's been millennia since the other last felt the light of another angel. Castiel instinctively reaches back, soothing him with not alone and memories of homelovelight. Lucifer drinks everything in, giving back not alone either and lovelovelove.
When Lucifer breaks the kiss, their wings and grace are still tangled together. Castiel blinks, then lifts a hand and places it on the other's cheek. "Your vessel. Nick. He's healed." The vessel is still marred with wounds, but they look much better now than they did when Lucifer first arrived.
"By your doing, Castiel," murmurs Lucifer. They remain in the same position, standing in each other's personal space, shivering when their wings brush over one another.
"You once said," Lucifer rasps, voice low and rough with emotion, "that we have a choice. We have the freedom to do whatever we want."
Castiel inhales, the air thick with hope and anticipation. "Yes."
"Then tell me, brother, what are my choices?"
A prophecy shatters into oblivion.