This story starts at the end of session 5 episode 19 Hammer of the Gods and what happens to Sam, Dean and Cas is cannon until the end of session 5, though you will find that the first few chapters will concentrate on what has been happening with Gabriel while they went about getting the rings and so on.
This is my first fanfiction so I hope you like it. Please feel free to review and enjoy.
Disclaimer: I do not own Supernatural (or any lines I have taken from the show), if I did Destiel WOULD be cannon and Cas would never have gone bad.
Lucifer stands talking to the Gabriel in front of him
"I know you think you are doing the right thing Gabriel, but I know where your heart truly lies."
With that Lucifer turns and stabs Gabriel through the heart with his own angel blade, causing his grace to explode out of him and his body to fall to the ground with the pattern of his wings burnt out around him.
In a room further down the corridor a short man is desperately doing an enochian spell, just before he completes it he stops and waits. The flash of dissipating grace radiates through the building.
"Finally" He whispers and with a final world the sigils on the windows glow and he throws himself through.