Unforgiven

Sam and Dean head to Bristol, Rhode Island to investigate why three women suddenly went missing, and discover that their grandfather and Sam had worked on a case together, in which men went missing, a year beforehand.

Sam's memories start coming back, including beating up a cop and sleeping with some of the witnesses (who turn out to be the missing women). But after he's recognised by the policeman he attacked the previous year, he's thrown into jail. Brenda, the wife of the town's former Sheriff (Roy) then releases him, believing he is suffering from memory loss.

Sam finally recalls the old case, which involved an Arachne, a half-human, half-spider creature that Roy helped Sam and his grandfather track down, before Sam was forced to kill him after he was infected by the creature's poison.

It then transpires that Roy is still alive, though hideously scarred, and that he lured Sam back to the town to get his revenge. Trapping the brothers in a web, Roy tells them that the Arachne species is spreading far and wide. Dean then manages to cut himself loose, while Brenda frees Sam, who then decapitates Roy.

The episode ends with Sam telling Dean that he feels very guilty about the dark deeds he did when he was soulless and wants to make amends. But to do so, means he has to start remembering everything.