The "cult" of Castiel is growing and his forces appear to be getting the upper hand in the angelic civil war, but now some are taking things a bit too far and turning themselves into angelic suicide bombers!
While Sam and Cas pursue a missing angel, Dean follows up on the suicide bombings. This leads him to Tessa (Lindsey McKeon), the reaper last seen in Appointment in Samarra, and he quickly discovers that she's bought into the whole "blow yourself up" deal, claiming it was Castiel who told her to.
All this legwork and misdirection is set against Sam's increasing concern over the influence the power of The First Blade - and the Mark of Cain - is having over the increasingly volatile Dean.
This comes to head in the closing scene of the episode, where our heroes are offered assistance by an unexpected source and Dean goes loco.
A focused and engaging episode, Stairway To Heaven sets up next week's season finale perfectly - with both Dean's descent into madness and the angelic war coming to a head.