With Cas off hunting down Cain, the Winchester brothers are left to work another case: a frat boy driven off a bridge by his "possessed" truck.
By the time Sam and Dean arrive on the campus a series of other mysterious murders are taking place: a girl is strangled by a computer cable and a boy has his brain liquefied by overly loud music!
Despite one clue leading the brothers to Corey Silver (Barbara Kottmeier), the widow of a car crash victim, the Winchesters struggle to put the pieces together and figure out the ghost's motivation, and how it is seemingly moving from object-to-object rather than being anchored to one particular item.
Ghost stories in Supernatural are always the best. It's what launched the show and its the type of story that always brings the horror.
For instance, Halt & Catch Fire had some delightfully creative death scenes that conjured up a definite Final Destination karma vibe.
Even after ten years, the show is still finding fresh ways to tell this style of story, but the one element that stopped this being a perfect episode was the Winchesters' inability to immediately grasp the obvious connection between the car crash and the murder victims.
It was a blindingly obvious deduction, especially given the details of the first death (once the angry spirit of the frat kid's brother had been ruled out).
Nevertheless, that minor glitch aside, Halt & Catch Fire was another superb ghost-themed episode, that also managed to bring a degree of temporary resolution to Dean's ongoing inner-demon conflict, resisting the Mark of Cain.