[s4e21] When The Levee | Breaks

: The title is a nod to a 1929 blues song famously covered by Led Zeppelin in 1971.

: Faces internal conflict after being ordered to sabotage the brothers' efforts, ultimately capturing Anna Milton when she confronts him about his actions. Lore and Production Details

: During withdrawal, Sam suffers intense hallucinations, seeing himself tortured by the demon Alastair , being accused of betrayal by his 14-year-old self , and receiving misguided encouragement from a vision of his mother, Mary .

: Under orders, Castiel surreptitiously releases Sam from the panic room. After a tense standoff where Sam dares Bobby to shoot him, Sam escapes and reunites with Ruby to consume more demon blood.

: Directed by Robert Singer and written by Sera Gamble. It is one of only three episodes in the entire series where no characters die.

" When the Levee Breaks " is the 21st episode of Supernatural 's fourth season and the 69th episode overall. Premiering on May 7, 2009, it serves as the penultimate episode of the season, directly setting the stage for the apocalypse.