Supernatural - On the Head of a Pin Season 4 Episode 16

Someone found Lucifer's sword and is using it to kill angels. Castiel and Uriel have captured Alastair and ask Dean to use the torturing skills he learned in Hell to extract information from him so they can stop the murders. Sam is concerned Dean can't handle the job but Dean agrees to do it. However, when Alastair reveals some shocking information, Dean's world is shattered.