A plot bunny entered my head the other day. Basically, the Doctor and Cas talking about humans, then realizing they were both discussing humans with someone who was not human. This is early Season 4 for Supernatural, and between series 2 and 3 for Doctor Who, just before the Doctor meets Martha.

Disclaimer: I own neither Doctor Who nor Supernatural. If I did, SuperWho would have happened already.

The Doctor sat on a park bench, deep in thought. So deep, he did not hear the rustle of wings, or realize that someone was suddenly sitting next to him.

The stranger was quiet at first, watching a group of people celebrating a birthday party.

"Aren't they beautiful? Humans." He spoke up, a hint of fondness in his voice.

The Doctor agreed. "They live so much. They do so much in their tiny lifespans."

"And even though they aren't perfect-"

"They try. They try, and as foolish as they can be,-"

"They are my favorite."

"Mine too."

A brief pause, then

"You are not human."

"Well, neither are you." Reaching into is coat pocket, the Doctor pulled out a small metallic object and scanned his park bench-mate. "You're..." he glanced at his screwdriver. "I don't know what you are."

"I am an angel of the Lord."

"An angel! That's brilliant! A real, live, angel!" The Doctor grinned widely, almost maniacally.

"What are you?"

"I'm the Doctor, a Time Lord. And your name?"

"Castiel."

"Castiel, an Angel of the Lord. I've never met an angel before. Well, Weeping Angels, but they don't really count."

"And you are a Time Lord. The title you chose-doctor-very admirable."

"Thank you. You know, I don't get that many compliments on my name. More jokes."

Castiel titled his head slightly, looking a little more squinty-eyed. "But doctor is a respectable title. You chose to be recognized as one that saves people."

The Doctor grinned and shook his head, changing the subject. "Castiel, have you ever traveled through time?"

"Yes, time travel is one of the abilities angels have."

"Oh." The Doctor deflated slightly, then grinned again. "Well, what about traveling to different planets?"

"I do not do that often, but yes, I have before."

"Oh. Would you like to travel with me anyway? I can take you nearly anywhere you want."

"I would like that, but I cannot. I have to protect a young man in order to prevent the apocalypse."

"Oh. That...sounds important."

"It is."

"Well, perhaps next time then."

Castiel smiled. "Yes, I'd like that."

The Doctor got up to leave, then paused and turned back to Castiel.

"I'm sure I'll see you around Castiel. Allon-zy!"

Well? It's not much, but I needed to write something. Did you love it? Hate it? Should I add more? Throw in a Winchester or something? Let me know in a review!