Dean hadn't been able to sleep lately. He couldn't stop thinking about the mark and what it was doing to him. He finally decided that he gave up. He got out of bed and walked to the kitchen to get a drink, but stopped cold when he heard the faint sound of a piano playing. He went back to the bedroom and grabbed his pistol. Headed towards the sound, Dean walked quietly down the hall. He thought about waking up Sam, but given the way things had been going between them lately, he decided against it. He made his way down the hallway and the music was getting louder and he eventually came to what looked like a dead end. Dean placed his ear against the wall and could hear the music on the other side. It was a beautiful song, but very sad, and it rocked Dean to his core. He placed both his hands against the wall, and to his surprise, the wall silently slid open. Dean pointed the gun out in front of him and walked into the room. When he got in, the door slid shut behind him and he lowered his gun. There was a single piano in the middle of the room, and playing the piano was none other than Castiel. He stood there listening to Cas play. There was so much emotion in the music that Dean stood there for a few minutes, a single tear rolling down the stubble of his cheek. Cas finished the piece and said
"I'm sorry Dean. Did I wake you?"
Dean started to answer,
"How..."
"Did I know it was you? I AM a celestial being you know. I heard you when you left the kitchen." Cas said with a chuckle.
"Come sit next to me."
Cas slid over so that Dean could sit next to him on the small piano bench. He started to play softly again.
"When did you learn to play the piano Cas?"
"I'm thousands of years old Dean, I've played for a long time," Cas said with a smile. "I just happened to find this room and decided to play. I really didn't mean to wake you."
"It's ok. I haven't been sleeping much lately."
"It's the mark isn't it?"
"Yeah," Dean said. He thought about lying, seeing as how last time they talked about the mark, it hadn't ended too well, but he figured what was the point in lying to Cas. Cas started to play a different tune. Slower, and darker than the last two.
"Did you write these songs?"
"Yes. This one is about you," Cas said as he continued to play.
Dean sat there, listening to the song, and closed his eyes, getting lost in the music. But then, his arm started to feel warm and he looked down, rolling the sleeve of his shirt up. The mark was glowing red. He turned to Cas and immediately shot up off of the stool. He couldn't believe his eyes. Lucifer himself was sitting in the spot where Cas just was. He continued playing, not missing a beat, as he turned to Dean and said:
"Didn't I tell you we would always end up here? So, tell me Dean....How does it feel to have my mark on your arm?"