Returning to her hometown of Purgatory for her uncle Curtis's funeral, Wynonna Earp— descendent of Wyatt Earp himself— runs into a little trouble on the Bluntline bus. One of the passengers, Kiersten Lesko, has left to go relieve herself in the woods, and falls prey to a ferocious and invisible demon, known as a Revenant, that can take on human form — a.k.a ugly. Wynonna goes to find the endangered passenger, but only succeeds in locating her decapitated head, and the demon that severed it. Wynonna thwarts the Revenant with some agile fighting skills before notifying the police and walking the rest of the way into town. Home sweet home.
Back at the scene of the crime, outsider Deputy Marshall Dolls interrupts Sheriff Neadley's investigation to pick up clues as to who might have killed the passenger (and three other young women in the town). And at the local Purgatory watering hole Shorty's, Wynonna runs into some old drinking buddies…and old drinking enemies. One of them, Champ Hardy, takes a real shine to her, and invites her back to his place thinking he's going to get lucky. (Yeah right, pal.) What he ends up getting is a switch blade at his throat, and Wynonna demanding he spill the details about her uncle Curtis's death: turns out when the body was found, it was missing a head too.
Suddenly, Champ's girlfriend bursts into the room holding a shotgun and starts firing shots at her cheating beau and his mistress. When the smoke clears, Wynonna recognizes the girlfriend as her sister Waverly: things aren't awkward at all. Waverly and Wynonna haven't seen each other in three years; but in that time, Waverly fears, a curse has returned upon the town just in time for Wynonna's birthday: a curse which only she can put an end to. But before they get underway, Deputy Marshall Dolls — who's come gallivanting into town — wants a word with Wynonna.
In a one-on-one, Wynonna learns that Dolls is with a secret branch of the U.S. Marshalls that handles unexplainable phenomena (call them the "U" files). Small wonder he's investigating the mysterious deaths by decapitation in the town of Purgatory, and if Wynonna has any connection to them. After the law leaves, Wynonna pokes around her childhood home; a trip that brings back some hard memories. Like when her father had to beat back the Revenants of outlaws Wyatt Earp once put in the grave. Like how those same demons ran off with her eldest sister Willa and slaughtered her in the hills. And like how Wynonna accidentally shot and killed her father while trying to save him from the demons. Wynonna's great-grandfather Wyatt's pistol "Peacemaker" is the only weapon that can return the risen dead back to where they belong — and Wynonna's got to fetch it. But will she lead a band of thugs to it as well?
Wynonna's aunt Gus McCready, Curtis's widow, urges Wynonna to take her sister and leave town, but our heroine will have none of it. Instead, she doubles down on danger, and retrieves Wyatt's Peacemaker from the dried-up well (and, shortly after, we see a hand with a distinctive ring emerge from the well. What's up with that?). She's paid another surprise visit by the tenacious Deputy Marshall Dolls, whom she warns not to follow her or her sister again. Peacemaker in hand, Wynonna stops along a remote road for target practice: she's rusty, to say the least.
Poking around Waverly's bedroom, Wynonna learns that her sister's built up quite an appetite for breaking the Earp family curse. Waverly wants to use Peacemaker to beat down the revenants, but Wynonna won't let her endanger herself. To settle her nerves, Wynonna haunts the bar, where a dandily-dressed stranger shows particular interest in both Wyatt Earp and his gun. We'll come to learn that this stranger is a man by the name of Doc Holliday, who was Wyatt Earp's right hand man, now come back to make nice with all the outlaws he helped kill. It also appears - based on the ring on Doc's finger - that this is the dude that came outta the well. It's a regular, weird, extended family reunion up in Purgatory.
When Wynonna returns to her aunt's place, she finds Gus has been brutally beaten by the gang. Before she passes out, Gus tells Wynonna that they've taken Waverly. Wynonna wastes no time in tracking her down. Wynonna finds her sister…with a noose around her neck, almost hanged, at their childhood home. Revenant Malcolm Ramaker and his posse of returned dead have got the place on lockdown. They strike Wynonna a bargain: Peacemaker, or her sister's life. Wynonna introduces a third option. First she lures one of the Revenants to a motorcycle, which she promptly explodes. Then, with a single ricocheting bullet she sends Ramaker back to hell and shreds the rope to set her sister free.
But Wynonna forgot about the third Revenant, and is all out of bullets to subdue him. Just in the knick of time, a shot coming from up in the hills takes out the demon — but no one can figure out who shot it. Perhaps it was the stranger from the bar earlier? Deputy Marshall Dolls descends on the scene, albeit just a tad late, and provides shelter for the sisters. Dolls puts it straight to Wynona: unless she wants to be tried for homicide, she's got to team up with him to defeat the Revenants. Wynonna has no choice but to fall in line.