Our Lives Are Different, but We Belong

Sam and Dean discover that they have a seventeen year old sister; and they agree to let her join them with the hunting and pre-apocalypse business. But Castiel reveals that Casey can be used in the fight against Lillith.

However, does Castiel have the heart to tell them what needs to happen? Will the Angles be far behind Castiel?

Set during season 4- before the last episode!

Disclaimer: I do not own Supernatural (sadly) I only own the plot and Casy :)