S5E15 : Dead Men Don't Wear Plaid

Sam and Dean investigate Bobby's home town where the dead are rising from the grave but instead of attacking humans, they are happily reuniting with their families. The brothers turn to Bobby for help but he tells them not to worry about it and to leave town. Suspicious, Dean investigates and comes face to face with Bobby's dead wife, who has no memory of what happened to her. Once the zombies start turning evil, the boys tell Bobby he has to kill his wife but he refuses.