We start off in Ireland, where two parents are lovingly getting their baby to sleep. A loud screaming sound begins that only the father can hear. A creepy screaming lady (who the mother can’t hear) sweeps in and begins her attack. The mother creates and casts a spell to get rid of the creature, but not before she herself is fatally injured. The baby is left crying alone in her crib.
We then cut to present day at the bunker where Sam is having trouble sleeping and having nightmares of his visit with Lucifer, namely the highlight reel of failures. Dean catches up with him in the morning, where we establish it’s not only been days since their visit with Lucifer, but that they’ve not heard from Cas either, leaving them blissfully unaware that Lucifer has now taken over Cas’s vessel. Dean suggests they look into a possible case at an old folk’s home not too far from the bunker to help Sam get out of his rut.
Meanwhile Cas/Lucifer (Cassifer) is at a park enjoying the day when he’s confronted by an angel who recognizes him as Lucifer. Lucifer tries to convince him he’s only there to help defeat the darkness, but the angel is having none of it so Lucifer has to kill him. He then complains that some angels have no vision.
At the old folks home the boys investigate the death of a man who was killed in his room, with the door locked. He had been screaming that he heard something and to make it stop before he was killed. The circumstances are almost exactly the same as the one in Ireland at the beginning of the episode. Later the next night the manager also hears the screaming, sees the banshee and is killed by the same creature from the beginning. Mildred, one of the residents, witnesses the banshee killing the manager.
Sam and Dean return and after a little digging, based on Mildred’s description, realize they are dealing with a banshee. It feeds off victims deemed "vulnerable" at night and can be killed by a gold knife. Dean heads back to the bunker to retrieve one so they can get the banshee that night. Sam stays behind to narrow down who they think might be the next victim, who turns out to be Mildred (who has taken a shine to Dean). Sam comes clean about them being hunters and promises they will protect her. Sam also asks her if she knows the cleaning woman he met earlier, a young deaf woman named Marlene. Mildred tells him there is no deaf person working there that she knows of, but if there is she’d love to meet her and practice her signing skills since her grandson is deaf .
Sam goes out to try and confront the maid, but she is one step ahead and traps him using a symbol on the wall, thinking HE is the banshee. As it turns out she’s not only a hunter but she’s also the baby from the start of the episode, who was made deaf after hearing the banshee. Her mother knew the spell because her father was in the Men of Letters, which means she’s also a legacy like the boys. Her story checks out when Sam has Dean check the Men of Letter records while at the bunker.
Speaking of the bunker while there Dean runs into Cassifer. Dean notices Cas is off, but with Cas being Cas and all, Dean doesn’t take it too seriously when he is acting weird. Cassifer tells Dean he’s there looking for a spell to draw Amara out. Over the course of their chat Dean confides to Cassifer that he is connected and attracted to Amara. And that he’s afraid he won’t be able to resist her much longer. Cassifer is intrigued, and as his wheels spin we have to wonder if Dean being used as bait is not quickly becoming part of his plan… but that’s for another day.
Dean heads back to the old folks home where Mildred, Eileen, and Sam are all awaiting nightfall and the arrival of the banshee. Eileen and Sam talk growing up as hunters and how revenge, like what Eileen is looking for in killing this banshee, the one who killed her parents, won’t really solve anything. Mildred invites Dean to watch the sunset with her and asks, “When was the last time you watched sunset without waiting for the things that go bump in the night to come out?” She sees he’s troubled and tells him the secret to life is to follow your heart, and the rest will work out.
The banshee arrives right on time, but instead of going after Mildred she heads straight for Dean (the vulnerable one of the group?). Mildred is able to use the symbol Eileen used earlier to trap it and Eileen is able to kill it. All is well and the boys say their goodbyes (I am definitely hoping we come across these two characters again someday).
At the bunker, the boys decide that Cas (Cassifer) is probably just acting weird after the time spent with Lucifer. Sam then tells Dean the truth about his trip down failure lane with Lucifer and apologizes for not coming to look for Dean when he was in purgatory (we have been waiting for this sincere apology for like 4 seasons!).
Before going to bed Sam wonders why the banshee went after Dean - who plays it off and claims it was really after Mildred. But as we watch Dean lie awake in his bed, we can tell by the look on his face, he knows the banshee had come for him.