What if the Yellow-Eyed Demon hitched a ride back to the future with Cas and Dean?

The Yellow-Eyed Demon pulled Mary in for a kiss to seal their deal. She was his favorite so far. He seriously wanted to breed with her himself, but that was against the rules. Lucifer needed pure human children with demon blood dripped into them.

He heard a car pulled up and looked up to see future-boy pointing the Colt at him. He had lost track of that thing decades ago and wondered where that stupid kid had found it. Just as he raised the gun to point it at him, an angel popped up beside him. The demon wasn't surprised. He didn't know of anything else that could pull off time travel. Angels. He hated them. They thought they were so much better than demons.

There was something surprising to the demon, though. The angel appeared to be whisking future-boy back to the future before he could shoot. The demon wanted to check out the future, so he rushed over and ended up sucked through the time vortex with them. Dean and the demon closed their eyes against the bright light and when they opened them up again they were back in Sam and Dean's hotel room, along with the angel.

"You weren't supposed to do that," Castiel said. "I must send you back."

"Why not let me kill him?" Dean asked.

"That would mess up the space-time continuum. Even angels aren't allowed to do that," Castiel explained.

"Why not?" Dean asked.

"Didn't you watch the Back to the Future movies?" Castiel asked.

"The what?" the demon asked.

"Yes, did you?" Dean asked, ignoring the demon.

"Yes. It was required watching. I saw them about 3,000 years ago."

"Those movies are only 25 years old," Dean protested.

"You still don't understand the concept of time travel, do you?" Cas asked.

Castiel reached his hand out to send the demon back where he belonged, but the demon evaded his grasp and disappeared out into the night.

"So, has the past changed?" Dean asked. This would definitely be a good thing. His parents would still be alive. Sam would have a normal life. He wasn't sure how this would affect him since he remembered everything, but maybe he had a wife and kids somewhere.

"I don't know. I'll check to see what's going on."

Castiel disappeared and reappeared 5 minutes later. "No, another demon took his place and everything happened exactly the same. I guess it won't mess up the space-time continuum after all. You can kill him."

"Great, except that now we don't know where he is," Dean pointed out.

"I can find him," Castiel promised. "But you don't have the Colt anymore. When we left I zapped it back to Daniel Elkins. You'll want it there later, correct?"

"No, I don't care. If I kill the Yellow-Eyed demon now I won't have to do it then."

"You'll have to kill his replacement," Castiel pointed out.

"This is going to get confusing," Dean said. They Ruby's knife. Hopefully that would be enough.

SSSSSSSSSSSSSSSSSSSSSSSSSS

When the demon zapped out into the night, he decided to try to find someone. His wife had been in Hell, unable to escape since they died. He had had a chance and taken it, leaving her behind. He hoped she wasn't mad at him. After all, she would have done the same thing.

He tuned in his built-in radar and smiled when he found her, and close by, too. He zapped to her location. She was standing there, next to a human. They had a demon tied up.

"What the hell?" the human asked.

The demon started walking to him, when the human put out his hand as if to stop him.

"That won't work on him," Ruby warned.

"Who is this, Ruby?" Azazel asked.

Sam noticed that the demon's eyes were yellow. "Is this a demon? I've never heard of one with yellow eyes?"

"This is the only one," Ruby said. She couldn't believe it. Nobody had heard from him in over 30 years. He had made deals to get access to kids and disappeared, necessitating another demon to take over.

Ruby was right about his psychic thing not working. The demon walked over to him and sniffed. "One of my psychic kids, then."

"Not yours," Ruby said. "Caspar's"

"That hack. What was he up to?"

"You disappeared back in 1973 and he finished your deals for you," Ruby explained.

"Oh, yeah. I just came from 1973. Hitched a ride with an angel and some other guy."

"Ruby, what's going on?" Sam asked. She seemed awfully chummy with this demon and they were talking about the psychic kids, like he was the mastermind of the whole thing.

"Yes, Ruby. What is going on? How is our plan going to set Lucifer free? Is this what you're doing now? Training him so he'll be ready for Lillith?"

"Shut up," Ruby said, but she knew it was too late. Sam wouldn't trust her, even if he didn't have all the details.

"Why?" the demon asked.

"I have to go," Sam said and started backing towards the exit.

"Can't let you do that, Sammy," Ruby said. To Azazel, she said, "You've ruined everything."

"How?"

"I was manipulating him, tricking him. Now, he won't trust me, because of you," Ruby explained.

"You do everything the hard way," Azazel said and flung Sam into the wall, just as he was about to reach the exit. He grunted in pain at the impact.

"What do you mean?" Ruby asked.

"You'll see. Do you know of a place where we can hole up?"

"Sure," Ruby said.

"Let's go now."

They walked over to Sam and Azazel and Ruby held hands and put their other hands on Sam's shoulders. They disappeared to Ruby's hideaway. It was hidden from demons and angels, and had warding off symbols so angels couldn't get in. They would be safe there.