More than 20 years ago, a mysterious demon killed Dean and Sam's mother, and father John began to train them as fighters. After John disappears, they embark on a ghost hunt, driving a 1967 Chevy Impala against mysterious forces across the United States. In the battle, his father and Sam died one after another, and Dean made a deal with the devil to exchange his life for the resurrection of his younger brother.
In the third season, the brothers have been trying to find a way to break the devil's contract in the one-year time limit, but in the end, Dean still can't escape the fate of falling into hell.
Season 4 takes place four months after the end of season 3, and we get to see what Sam has gone through after he leaves Dean, and what happens to Dean in hell. For four months, he lived alone without his brother and lost contact with Bobby and others. It can be said that during this period of time, Sam has given his life to investigate every case, and is fighting for his life.
This season expands the world of Supernatural to try out more different types of things. One episode, for example, will be shot in black and white as a tribute to the horror films of the 1930s.
