Well, we're not saying having vampires in your town is necessarily a bad thing. But often it can lead to shortened parties. All these bodies seemingly died simultaneously, and then were arranged in this strange formation. Hawt's intel has it that these massacres have a history: they're the calling card of the Cult of Bulshar.
And while Doc is tending his bar, an eerie fog rolls in, the other patrons are taken out, and he himself is swept up by a well-placed rope, and whisked away. Free drinks... but there's no one to sling them.
Wynonna needs help to find the culter(s) who may have slaughtered all these people. Wynonna drops in on her mother — who's now hearing voices — at the penitentiary, looking for some answers. She doesn't get any.
Wynonna voices her concerns for her mother's health — and by voicing, we mean demanding — and Dolls shows up to provide some backup. He'd been following her while she made these visits to her mom, and now he wants to help her get to the bottom of the mistreatment Wynonna's mother has been subjected to.
Meanwhile, Doc is being tested by one of Petra's vamps. They want to turn Doc, make him a valuable asset to the team. But first they've got to prove it's really him. When he doesn't cooperate and he recognizes the veiled woman, he gets knocked out.
Wynonna returns home, finds a vampire hiding out in the shed, and alerts the other members of her squad. Of course, they've all been glamored, and don't take kindly to her alarm, and Nicole knocks her out.
The vampires throw a party as they prepare for the return of the head vampire honcho. Also, they've invited all their glamored acolytes to enjoy their last night on earth. Everyone's toasting with a glass of blood in their hands, except... well, Wynonna...
She's trapped in a coffin, prepared as an offering. Dolls happens to find her in the cellar and set her free. They're the only two not under the vampire spell, and hence the only two who can reverse it. Dolls has a book on black magic, a tutorial on the counterspell. It involves lots of wooden stakes.
The two crash the party, and while Wynonna distracts the vampires, Dolls drives projectile stakes through their hearts. Petra's the first to go. From then on out, the spell is lifted, and it's a bloodless bath — the vampires turning into straight dust.
And while Wynonna takes Waverly on a drive to tell her about their mother, the car skids off the road, flips over, and rolls down a slope. Waverly is shortly thereafter dragged from the car by an unseen figure, who, we're just going to guess, is not a paramedic.