"Dean, Sam and Castiel deal with Cain’s return. Crowley and Rowena continue to grow closer but when Crowley bails on plans with his mother to help the Winchesters, Rowena lets him have it."
So Cain is back, and murdering again. Dean is the only one who can stop him and is forced to use the "First Blade" to kill Cain. Cain said that Dean will end up killing his brother, Sam, just as Cain killed his brother, Able. And now Dean has been killing with the first balde again which drove him evil in the first place. Not looking good for the Winchesters future.
