"Old Souls" starts off with a flashback to a bloody wedding, where a bride wearing a certain dress takes an ax to her loved ones before killing herself. We then cut to the present day, where everyone is getting ready for the WayHaught wedding (so many pretty flowers!), and we find out that Waverly (Dominique Provost-Chalkley) has purchased the murderous dress from the flashback.
Shenanigans ensue in typical Earp fashion — Wynonna (Melanie Scrofano) tries on the cursed wedding dress and then can't get it off. (It also blows up the wedding cake and causes the wedding arch to catch fire, as cursed dresses tend to do.) Wynonna runs to Doc (Tim Rozon) to get help, and the two end up talking about their relationship while trying to get the witch who sold Waverly the dress to remove the curse.