Dean is devastated by the death of Kevin and wants to get the traitorous angel Gadreel out of Sam as quickly as possible.
Unfortunately, after confiding in the newly powered-up Cas, he realises that the only course of action is to strike a deal with Crowley.
Post-haste, the king of hell is released from confinement and the trio set off to track Sam/Gadreel down.
However, Crowley walking the Earth again quickly draws the attention of Abaddon, who sets out in pursuit of Crowley and co.
Having captured Sam, Crowley's attempt to hack into the younger Winchester and encourage him to eject the angel fail (although he does, rather gruesomely, get to turn Sam in to a minor league Pinhead).
It is then, when Dean suggests that Cas possess Sam to drive Gadreel out, that Crowley reminds Dean and Cas of the difference between angels and demons - angels have to be invited in when they possess a vessel, but demons aren't so polite.
Road Trip was another cracking episode of Supernatural, although by season nine, unsurprisingly, these are the norm and it's the odd weaker episodes that stand out (which these season has yet to throw up).
It took the season's main arc and, once again, ratcheted things up several gears, simultaneously bringing the Winchester brothers back together and driving a massive wedge between them.
Crowley is now free, Gadreel is still on the loose and civil wars are brewing in both Heaven and Hell (although the angels' war has already proved itself quite bloody, Crowley is more inclined to hold onto the throne of Hell with a well-run political campaign!)