Southern Comfort

S8, E6: Investigating a murder, Sam and Dean find that Garth (guest star DJ QUALLS) is already on the case. While Dean's not happy to learn that Garth has assumed Bobby's duties, Garth points out that both Sam and Dean have been missing for the last year and someone needed to do it. They guys discover an "avenging ghost" is responsible for the murders and they need to find the source before the killings starts again.