So this takes place in an extremely hypothetical situation in which Sam, while traveling independently from Dean in between "Good God, Y'all" and "Free to be You and Me," met up with the Doctor and had a couple of adventures with him. In this ficlet, the Doctor confronts Samifer, and tries to pass on a very important message to the human inside.

Clash of the Titans

Sam was waiting for him. The Doctor stepped outside of the TARDIS, shrugging on his coast, and came face-to-face with the younger Winchester - 'No,' the Doctor corrected himself sadly, with the Devil Himself. (Well, one of the Devils Themselves. He'd met quite a few over the years.) The angel used Sam's eyes to look on the time machine with wonder and amazement, before turning on the alien. The angel's senses were so much more than a human's, and the Doctor knew that he could really, truly see him, not just his current regeneration, but the memories of his past lives and the shine of residual artron energy. The angel's awe increased, eyes widening in a mockery of Sam's own expressions. When Sam had first met the Doctor, he had been so earnest, so hopeful, so eager to learn. The Devil was none of this; he was cunning, and patient, too. The Doctor stuffed his hands inside his pockets, surreptitiously grasping the sonic screwdriver and locking the TARDIS door.

Just in case.

"Doctor," the angel said, all reverence and respect.

"Lucifer," the alien replied, tone carefully flat.

"I have heard," he said slowly, flatteringly, "so much about you. Sammy here thinks of you a lot. You left quite the impression on him."

"Oh, did I?" The Doctor didn't stop for an answer. "The right one, I hope. Don't think it would be too beneficial for him if he picked up my driving skills. Or cooking skills. Or penchant for running away. Although, that last one might actually work out in his favor."

Lucifer chuckled, soft and measured. "I believe it was the universal compassion and the massive guilt complex." The Doctor had been feeling the effects of said guilt complex too long for him to visibly flinch. Lucifer caught onto it anyway. "To be honest, I think he might be in love with you a bit. All that knowledge and agelessness, and those big hearts of yours… Too bad he doesn't know about what you did to your planet, hmm?"

"May I speak with Sam?" he asked, studiously ignoring old and painful memories. Permission was very important to both species, but especially to the angels, the Doctor understood.

Lucifer grimaced slightly. "Well, he can hear you, if that's enough. I just got this body," and here he spread his arms as if showing off a new fancy suit, "I'm not really keen on giving it up right now." It was a lie - Lucifer could easily release Sam's voice while continuing to occupy the rest of him. But even as the Doctor wondered if he should correct him, Lucifer ignored him, caught up in his admiration of Sam, of himself. "Sam is so beautiful, don't you think? This body is so strong, so powerful, and his soul…" Lucifer sighed in pleasure. "So kind. Sammy's just the nicest, most selfless person ever. Do you know why he said 'yes' to me?" The Doctor knew only the version he had read about before the Time War; Romana used to discuss the reason why with him often during their travels. After the War, everything changed. This was brand new territory, a new timeline stretching out into infinity. He had no idea why Sam said yes. He let Lucifer continue. "He was going to throw himself into the Pit, taking me with him. Isn't he wonderful?" The Devil smiled gently at him. "It's a shame that no one ever saw it."

If that had been anything else other than a sly implication that the Doctor was incapable of connecting with those who traveled with him, he would rummage around for that old seven foot scarf, and eat it. Without salt.

He supposed that the Devil was only used to manipulating humans. He was sure that, had he been human, the Doctor would have been flustered out of his skull, confused and tripping over himself. As he was now, alien and all, he was only mildly irritated. For himself, that is.

He was furious for Sam.

"Then, may I speak at him?"

Lucifer shrugged. "I guess. He won't be able to talk back, you know."

"I know. As long as he can hear me."

"Suit yourself."

The Doctor stood before Lucifer, searching for some hint of Sam. A voluntary twitch, a subconscious moan, even just a spark of recognition in his eyes. But there was nothing. The angel had engulfed Sam so completely that the human was trapped within his skin, screaming inside of his own head where no one could hear him.

'Oh, Sam…' The Doctor felt his hearts breaking, because Sam was far too young to have a burden of this magnitude on his shoulders, and it was so important that Sam hear this and understand… "Sam? It's the Doctor speaking. Can you hear me in there?" Lucifer raised Sam's eyebrow. "I promise that I'm not a hallucination, or a trick. I'm here, I'm real, and I just want to tell you something." He paused again, waiting for a reaction. When nothing happened, the Doctor took a deep breath and continued. "Samuel, Winchester, I am going to do something that I haven't done in a very long time - I am going to have faith. I have faith that you are listening to me. So listen closely.

"This - Lucifer and the demons, the Apocalypse - this is not your fault. Do you understand me?" Lucifer smirked at him, no doubt tormenting Sam inside with twisted half-truths and playing off of his guilt. "You have been manipulated all your life by other people; this is no different. How could you have possibly known that Lilith's death was the final seal?"

"Is this going anywhere?" Lucifer interrupted smoothly. If his intent was to throw the Doctor off his guard, it wasn't very successful.

"As a matter of fact, it is. Now, I believe I was talking at Sam, not at you, so if you wouldn't mind?" Lucifer arranged Sam's features into something that could be mistaken for contrition, and then into a mask of serenity, crossing his arms. "Sam…" the Doctor stopped mid-sentence. What could you say to a person who was so kind, so thoughtful, so good, who had brought the End of Times upon his world through no intent of his own? What could you possibly say to him?

"Sam, I need you to listen to me, because this is very important. You are amazing. You really are. I have seen some of humanity's best and brightest and you outstrip them by miles. I only take the best, remember?" He took a step forward, intending to place his hand on Sam's shoulder. Lucifer retreated a step, eyes wary and mistrustful. But that step was… hesitant. Reluctant.

Got him.

"You're a good man, Samuel Winchester. You are brilliant. Remember that."

There was a moment of silence, and then, "Are we done?" Lucifer sounded bored out of his mind.

"Yep! Thanks so much for your time, I'd best be off now," the Doctor chirped, turning back towards the TARDIS. He unlocked the door, throwing over his shoulder, "You take good care of that body now - wouldn't do to damage borrowed property, now would it?"

"Wait - Doctor." The alien turned around, one foot in the door. The angel had bowed. "It was an honor to meet you."

"…Likewise." He slipped inside of the time machine, and shut the door gently. There was the sound of a wheezing, droning engine, whispers of gods long since dead, and then he was gone.

Lucifer stared at the space where he had been, a knot of uncertainty deep within his soul