Doc, Dolls, and Wynonna are the centre of attention as Bobo's party guests turn into a murder-crazed mob. Dolls and Doc toss Wynonna out the window (to safety) and prepare to fight their way out of the zombified crowd. Meanwhile, out on the border of Purgatory, Bobo and Willa are reminiscing about the time they used to spend with each other, and fantasizing about the time they're going to spend with each other as soon as they step over the Ghost River Triangle line together.
Unfortunately, without Peacemaker in her hands, Willa is helpless in safely guiding Bobo across the border. Turns out, before she left the party, Waverly switched the guns. So Willa, after being rejected by Bobo for a quickie, goes back to town to retrieve it. Back in town, Dolls and Doc, needing more backup, take Officer Haught into the Black Badge fold. While they attempt to locate and administer an antidote to all the crazies, she's to hunt down the Earp sisters.
Wynonna is at the homestead fending off a deranged townie when Willa comes in looking for Peacemaker. Her hunt is derailed when Wynonna gets a phone call from yet another deranged townie, this time it's the Sheriff's daughter Chrissy, who's got Waverly hostage at the police station. After springing Waverly free, Willa goes back on the hunt and pulls a gun on her sisters, threatening to shoot if they don't hand Peacemaker over. Office Haught comes in, and Willa aims the barrel at her: At Waverly's behest, Wynonna hands over the pistol, prompting Willa to take off.
Waverly and Wynonna go in search of their sister, and get ambushed in an alley by the antidote-seeking townspeople of Purgatory. Luckily, Sheriff Neadley suggests that maybe killing Wynonna is not the solution to their problems, and the Earp sisters narrowly escape in search of the serum. Meanwhile, Doc and Dolls bust into Bobo's bar in quest of the antidote as well, and start shooting up the place. Things don't turn out quite as rosy for Dolls as he takes a shot to the side. The only way Doc can save his life is by injecting him with his special medicine. Doc accidentally delivers an overdose causing Dolls to go into a roid-rage. Dolls and Doc then make short work of the guys in Bobo's bar, leaving the antidote unattended and theirs for the taking.
Waverly runs off to the tree house to intercept Willa, but finds only Bobo. She presses him for answers. When Willa was taken by the Revenants, it was Bobo who sought help from the Stone Witch to save the young girl's life — in exchange, he promised to search the land for Constance's sons' bones. Bobo's love for Willa grew, as did his admiration for all the Earps. Which apparently is a family Waverly is not a part of. While Waverly is still in turmoil, Willa arrives, and she and Bobo leave together.
Black Badge superior Agent Lucado and her team put the town of Purgatory on lockdown as they pump the antidote into the sickies. Dolls' boss tells him that she's got new orders: when Bobo opens the door to Hell, they're to observe and report. Sounds smart.
Out in the woods, Wynonna and Doc come upon Willa and Bobo as they attempt their escape. Some gunfire and grenade explosion render Doc and Bobo incapacitated, leaving Wynonna to knock some sense, literally, into her elder sister. But it seems that Willa is immune to rational arguments, and the two are locked in a semi-automatic chicken fight. When Willa crosses the Ghost River Triangle line, a giant beast is unleashed. With a heavy heart, Wynonna has to put her big sister down in order to save the town from the rogue Earp and the scary ass beast.
Later, Lucado and her team apprehend Bobo — to conduct testing on him — and Dolls — because he defied orders — and whisk them both off in the back of their truck. Wynonna chases them down, and with her unparalleled markswomanship, plugs Bobo, sending him to Hell. Dolls is going to have to find his own way home.
Wynonna, Dolls and Waverly are in dire need of some closure. They return to the site where Willa perished, and find a pool of black liquid left by the same monster that scooped up Willa. So, naturally, Waverly sticks her finger in it. This essentially turns her to the dark side, and all smiles she pulls a gun on Doc and Wynonna.