Supernatural S04E03
This will pick up the trail of the immortal and immoral Doctor Benton, who is tracking down his descendant, Michael.
Knowing they are a few days behind Michael and Doc Benton, the Hunters head north to the town mentioned in Michael's postcards, Boon, Michigan. The postcards are signed from a "Milan Carillo." This Milan may be someone Michael trusts, or a last-ditch Hail Mary for protection and hiding. Since Boon is tiny with few services, they opt to go to Cadillac, the county seat, along Lake Cadillac. This is still small, at about 10,000 residents, but as the county seat has the regional high school, library, county historical records, local hospital, and other services that might be useful in an investigation.
En route, the Hunters call their families and friends to warn them about corn syrup. This is particularly funny for Dr. Airy's family, as they can afford "real" foods and think he is just coming up with a new diet program. This is not a problem (yet) for Ciaran's relatives in Ireland, and Razik is estranged from his family.
Ciaran is, however, still driving Doctor Benton's stolen Mercedes. Jon Clarke enjoys an Enya free ride for once. The Hunters do a little bit of internet and Lore searching during the drive, scanning the news, weather, and some local history for anything worthwhile to check out later with the team. They find that there was a string of stories from the 1980s about people being attacked and missing organs or body parts, and being rushed to the hospital - they flag this as potential Doctor Benton. In terms of lore, there had been a notorious vampire nest in the area, out in the woods somewhere, but it was taken down during the great vampire purge in their parent's generation, probably by legendary Hunter Daniel Elkins in the 1970's or 1980's (of whom Johns Remington and Winchester would know and have worked with). The Hunters also contemplate how what the doctor did to himself and plans to do with Michael could be mad science or alchemy, but they refrain from hitting up sources that would know more about it, including Zach, who has the alchemical tome of Hans Reudi Von Steffan, Becky and Cassie's antagonist, or the Winchesters, who dealt with Benton last. They complain about cleaning up their messes, but this is honestly the first from Sam or Dean, not John or the forces of Heaven or Hell
Sam and Dean did not know about Castiel and Crowley's agreement to split the power of souls from Purgatory, but it was to stop Raphael from restarting the Apocalypse. Almost everything got back into Purgatory except the Leviathan, so the Leviathan is not Sam or Dean's fault; it's Raphael's RESTARTING THE APOCALYPSE.