Want proof that the war is Heaven is heating up? How about the arrival of an angel hitman, and an unfriendly one at that (but really, is there any other kind)? He'd better keep Cas out of his sights. Here's one heck of a spoiler, courtesy of TV Guide:
An angel hitman is coming and he's not a happy camper (think Javier Bardem in No Country For Old Men, Friendo). He'll cross into an alternate universe to catch his quarry, and when he does, the results will be bloody.