Sam and Dean enter a small town in Iowa, where three men have inexplicably beaten their wives to death. The guys realize that behind the murders is a Siren, a creature that can take different forms and desperately needs love and compels people to destroy themselves as a show of devotion. The Siren eventually puts Sam and Dean under their spell and pits the two brothers against each other in a fight to the death.

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.