Cas returns to the bunker to find Sam and Dean completely devastated by some bad news.
"Sam, Dean, what happened?" Cas asked as he looked back and forth between the two brothers, "You look awful."
"Cas, I don't know how to tell you this," Sam shook his head and the look in his eyes made Castiel's stomach drop.
When Sam didn't immediately continue Cas asked, "Where's y/n?"
Sam couldn't bring himself to say the words, so Dean got up from his seat and walked up to Cas, "I'm sorry, Cas, but Y/n is gone."
"What do you mean she's gone?" Cas asked as the whole world started to fall apart around him.
"She was shot," Dean told him, "On her way back from her last hunt she stopped at a gas station and some junkie tried to rob the place. Y/n tried to stop them but..." Dean couldn't bring himself to say the words, so he skipped over it, "by the time the ambulance got there it was too late. I'm sorry, Cas."
"No," Cas croaked as he struggled to control his emotions, "This can't be happening."
"I'm so sorry," Dean said sympathetically, "I know how much you cared about her."
"We have to save her," Cas insisted, "When have any of us stayed dead? That's not something we do."
"Cas, I don't see how we can bring her back," Sam finally joined the conversation, "You can't get into heaven and even if you could there's no guarantee the other angels would let you take her soul back."
"I don't care what it takes, Sam," Cas growled, "I'm going to get her back, even if it's the last thing I do."