While on the hunt for Lucifer, strange omens draw the boys to a small town in South Dakota, where they meet Don, an angel with a proposition... Don sends them a very long way, on a mission to find the secret the Devil never wanted them to discover.
Investigating recent reports of Biblical signs at a small town, Dean and Sam discover an angel, Don, who claims to have been the guardian of Lucifer's Cage. Unwilling to return to guard duty in Hell after witnessing life on Earth, Don offers to send Sam and Dean back in time to 1954 in order to recover the War Scroll, a scroll said to contain a battle plan for killing Lucifer, that was lost in New York in July 1954.
Although Sam and Dean are able to recover the War Scroll - aided by father-and-daughter Hunter team Walter and Julia Wilder - they are shocked to discover that the scroll's only information is a list of the bloodlines of Angelic vessels: the 'battle plan' merely consists of eliminating the Vessels so that the Angels can never manifest on Earth in the first place. Realizing that Don is really working for the demons - including Eisheth, an Angel who willingly became a demon out of love for Lucifer before she was trapped with the Scroll - Dean and Sam make a deal with Eisheth to return to the present day, provoking Don into fighting with Eisheth after she has possessed Sam before Castiel teleports Dean and Sam/Eisheth away, allowing Don to be smote by the other angels. Eisheth, as per their deal, takes another host and departs.