Supernatural Episode Details!

Episode 4x16 "On the Head of a Pin"

SOMEONE'S KILLING ANGELS

Someone found Lucifer's sword and is using it to kill angels. Castiel (Misha Collins) and Uriel (guest star Robert Wisdom) have captured Alastair (guest star Christopher Heyerdahl) and ask Dean (Jensen Ackles) to use the torturing skills he learned in Hell to extract information from him so they can stop the murders. Sam (Jared Padalecki) 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.

Source: CW

Pic:http://th03.deviantart.com/fs15/300W/i/2007/016/b/a/Dean_Winchester_Portrait_by_clefchan.jpg