Castiel found him in an abandoned apartment building in Pontiac, Illinois.
He felt the fear coming from not only Dean, but Sam. Gabriel even seemed a little worried now that Castiel knew the truth. The rebel angel, and his rebel son.
Castiel was spiraling downwards, and he didn't care.
Lucifer greeted his son with a smile. "I knew you would come Castiel."
"I had nowhere else to go." Castiel answered.
"You will always have a place with your father." Lucifer answered.
Castiel slumped against the wall. He did not trust the other angel. He didn't know what he was doing here. "Was this your plan all along? To isolate me so all I would have is you."
"I would never hurt you." Lucifer defended. "I never wanted to leave you. That was the hardest part about being kicked out of heaven.
Knowing my son would never know me. You of all angels have to see the flaws in heaven. The rules, the hierarchy. Our kind is little more than slaves to an absent god. All I wanted was to free them."
Castiel looked up meet his father's eyes. "Do you not realize the impact of what you did? What you created. All those demons."
"The demons are nothing but soldiers. When I defeat Michael they will be eradicated." Lucifer answered.
"I will not let you take the Winchesters." Castiel answered.
Lucifer frowned. "The Winchesters. The ones who never appreciated a single thing you did for them. The ones who feared you when they found out what you really are."
"They are my family." Castiel said moving to stand straight up.
"I am your family." Lucifer answered.
Little did Castiel know that what the fallen angel said would send him into a spiral of doubt. The way they looked at him, he was just a tool to them. Nothing more.
Castiel said nothing to his father. Not for the next hour, or the next day. Castiel was deep in thought, trying to find the truth in himself.
Lucifer did not push his son, he found the quiet proximity comforting. Grace of his grace.
Almost 48 hours later Castiel moved to sit across from his father. He took a deep breath and asked carefully, "What is the plan?"
Lucifer told his son everything, from the beginning. His story of when he fell, the demons, hell, breaking the seals. How he would isolate Sam Winchester, how he would get him to agree.
Castiel didn't think the plan would work for getting Sam to agree. However he had his own.
The only loose thread was that his father did not know what Micheal had planned.
Castiel and his father would have to get their information the hard way, sending Castiel spiraling further down.
Castiel spent the next few days watching his father torture lower angels. At first it made him squeamish, but he knew it was means to an end. If they couldn't figure out Micheal's plans then the apocalypse would continue. The heavens would rain down on the humans, they would suffer instead of just dying. To Castiel it was a means to an end.
Then Castiel was torturing his own angels.
First there was Jophiel, Peter, and even his friend Raguel.
Raguel begged him now to do it. He told Castiel that he could still see the light inside him. He told Castiel that he was the angel with the biggest heart, that he couldn't do this. He told Castiel he was nothing like his father. That he was good.
Castiel took pleasure in ending him.
With each torture Castiel could feel the wings on his back become heavier. The darkness was eating away at him.