S04E18: 'The Monster At The End Of The Book'

Sam and Dean are baffled to discover that they are the main characters in a series of underground books called Supernatural which appear to recount every moment of their lives.

Investigating further, the brothers soon learn that every argument, mannerism and mishap has been recorded in perfect detail, and no matter what they do, they cannot seem to change the future.

Tracking down the author Chuck Shirley, he insists that his characters are fictional and that they come to him in visions, leading the Winchesters to think that he might be psychic.

However, matters are further complicated when Shirley drops a bombshell about what will happen next in their lives - Lillith is coming for Sam and they will engage in the "throes of fiery demonic passion".

Dismissing the likelihood of that ever happening, Sam is adamant that they should stay and fight, while Dean would prefer to run away, prompting Sam to question whether Dean is really the same person he was before going to Hell.