On the trail of Bela to retrieve the stolen Colt, Sam and Dean track her to Monument, Colorado, only to find her motel room empty.
'How is she always one step ahead?' John wondered.
'She's actually quite smart.' Dean replied, begrudgingly.
Answering the room phone, Dean finds Bela on the other end of the line - already "two states away" and indicating that she's set them up.
'She always manages to get away.' Sam said, clearly annoyed.
Moments later, local police storm into the room accompanied by Special Agent Victor Henriksen - Sam and Dean are taken into custody and brought to the local sheriff's office.
'She called the police on you?' Mary commented, surprised.
'We never knew for sure but we assumed so.' Dean replied.
Henriksen makes sure that the barely-staffed small office is equipped as effectively as possible for the Winchesters, keen to not allow them to escape again.
'You two are clearly high profile criminals.' Jo said, with a grin.
Dean smirked.
He phones FBI Deputy Director Steven Groves, who insists on sending in a chopper to expedite them.
'Because we're so high profile.' Dean added with a smirk.
Sam and Dean are placed in a small holding cell and Henriksen comes to speak with them, bantering with Dean before telling them that they will be taken to a maximum security prison in Nevada and kept there until trial, and that this is probably the last time Sam and Dean will see each other ever again.
'That's not good. What plan did you guys create to get out of this one?' Mary asked with a grin.
'You'll see.' Dean replied, the grin melting off his face.
Groves arrives with the chopper and insists Henriksen fill out a copious amount of paperwork. He visits Sam and Dean in the holding cell and reveals that he is in fact possessed when he shoots Dean in the shoulder.
'That's gonna be hard to explain.' Mary commented, looking worried.
Sam fights him off and begins an exorcism, which is cut short when the demon vacates the host. Henriksen and others, alerted by the noise, rush in to discover Groves dead on the floor.
'Don't tell me they actually thought you killed him.' John commented.
They are confused by the lack of blood and have no choice but to believe that Sam and Dean did not shoot him, though they still do not believe the Winchesters' explanation that he was possessed.
'I wasn't expecting him to actually believe you.' Mary commented.
'He didn't have much choice.' Sam replied.
FBI agent Calvin Reidy goes outside to find out what's happened to the rest of the officers in the chopper, only to discover that they are all dead, throats slashed. The chopper explodes and Reidy is killed by another demon possessing one of the fallen officers.
'They have to believe you now.' John said, with a smile.
'Shame it took so many dead bodies.' Dean replied, sharply.
Panicking, the local sheriff wants to go outside and fight, but Henriksen realises that they are under siege and convinces them to all stay inside and barricade the doors.
'I've never seen so many demons in one place outside of hell.' John said, in wonder.
All communications with the outside world are down, and soon the electricity goes off as well. All that remain inside are Nancy Fitzgerald (the secretary), Sheriff Melvin Dodd, the deputy, Henriksen, and Sam and Dean.
'How much more will it take before they release you?' Mary questioned.
'A while.' Sam replied.
Meanwhile, Sam attempts to patch up Dean's bullet wound. Henriksen comes to the cell and confronts them, assuming that the siege is being carried out by their allies and unwilling to believe otherwise.
'Really? They still don't believe you?' Mary questioned. Sam and Dean sighed.
Shortly after Henriksen leaves, Nancy comes to the cell. Sam manages to convince her to bring them a clean towel to dress Dean's wound; when she hands it over, Sam grabs her wrist and steals the rosary from it.
'What was that for?' Jo asked.
'For exorcisms.' Sam commented.
Later, the sheriff unlocks the cell and comes in - he is keen to get everyone out of the station and to safety. A possessed Henriksen interrupts, though, killing the sheriff. Sam and Dean manage to exorcise Henriksen, using holy water made in the toilet with the aid of Nancy's rosary.
'Now he's got to believe you.' John commented.
'It took him being possessed for him to believe us.' Dean replied.
Following the exorcism, Henriksen believes Sam and Dean, and releases them so they can help fight off the demons outside. They put salt barriers up on the doors and windows and Sam paints devil's traps at key entry points.
'Thats's not going to keep them out indefinitely.' Cas commented.
Meanwhile, Nancy patches up Dean's gunshot wound. Dean goes to retrieve more weaponry from the trunk of the Impala, making it back inside just in time before a horde of demons descends upon the building. Unable to get inside, the demons possess the locals - about thirty of them - and stand around outside the building.
'You two have the worst luck ever.' Jo commented, incredulously.
Inside, Dean passes out protective charms that will prevent the others from being possessed. Sam and Dean reveal that they don't need the charms themselves as they both have matching tattoos of it, on the left side of their chests.
'That's actually quite cool. When did you get them?' Mary questioned.
While they wait and arm up, Dean and Henriksen discuss their respective lives and find they have much in common.
'Who'd have thought you guys would have so much in common?' John said with a smile.
Ruby shows up, able to get in through a salt line damaged unwittingly by the deputy.
'Oh no. What does she want?' Mary protested.
She tells them that the demons are from Lilith, Sam's demonic rival from "the west," and tries to convince Sam that the solution is a spell she knows that will "vaporize" all demons within radius - including herself.
'I'm assuming that there is going to be some kind of downside to it.' Cas commented.
However the spell requires the sacrifice of a virgin.
'Just as I thought.' Cas added.
Nancy volunteers but Dean is vehemently against the plan, convincing Sam instead that they need to just open the doors and fight off the horde themselves. Exasperated, Ruby leaves.
'Quite right. I'm glad you guys have some sense.' Mary replied.
Dean's plan is carried out successfully - Dean, Sam, and Henriksen fight the demons inside while Nancy and the deputy bar the doors behind them again, trapping the demons in the building - but not before one demon escapes.
'That demon must have told Lilith.' Dean realised, looking upset.
An exorcism pre-recorded by Sam then plays over the office's PA, sending the demons back to hell.
'That's really smart.' John commented, smiling.
In the aftermath, Henriksen promises Sam and Dean that he'll lie about what happened and say they were killed in the initial chopper explosion in order to get the law off their backs.
'That's decent of him.' Jo commented.
Pleased with the outcome, Sam and Dean leave. Not long after, Lilith arrives at the sheriff's office in the form of a young girl, looking for Sam and Dean. She destroys the building and kills everyone in it - including Nancy and Henriksen.
'Oh my god.' Mary gasped.
Sam and Dean later find out about it when Ruby turns up at their motel room and tells them to turn on the television, again rebuking them for not behaving appropriately under the jus in bello - i.e. "laws of war."