We open in medias res, as crazy cultists the Reasonabilists, whose remaining members still live in Pawnee, proclaim the end of the world anew every couple of years. Cult member Herb, who's stopped by the P&R office to talk to Leslie about using park space to await the arrival of Zorp the Surveyor, tells her they will all be freed of their flesh come dawn the next day.
Ron uses this as a money-making opportunity, selling hand-carved flutes and recorders to the believers (yes, post-dated checks are fine), while Leslie uses it as opportunity to try and force Ben to hang out with her for the first time since they broke up earlier in the season. Her plans face a challenge when reporter Shawna Mulwae-Tweep shows up to do a story on the Reasonabilists, but ends up with a small crush on Ben.
When Shawna asks Leslie what the deal is with Ben, Leslie describes him as a man who is also a worker and not someone that she has ever discussed sex with. Leslie vents to Ann "Just because I can't go out with him, someone else can?" and sets out to sabotage the flirting, and then it to the next level by forcing Ben to come with her to an abandoned gas station that she claims was owned by Mick Jagger in the '50s (and where Ben thinks an increasingly unhinged Leslie is going to murder and bury him). Ben calls her out on her plan and says they can't hang out as just the two of them, and Leslie reluctantly agrees.
Back at the park, Leslie confides in an unwilling Ron that if the world really were ending, she would want to spend it with Ben. That's great, says Ron in so many words, but the world's not ending. The following morning she shows up at Ben's house house and tells him that Shawna thinks he's cute and that she had no right to come between them, and his and Shawna's future children.
Across town, in the empty space that was Entertainment 7twenty’s HQ, Tom and Jean-Ralphio decide to use the final $10k they have left over (of the $450k they started with) to throw the greatest party anyone has ever seen. The entire party is a VIP area, with double and triple VIP areas and a centurion club elite VIP area, sponsored by Sobe Life Water that no one is allowed to enter. The perfect party, as held by "party scientist" Tom features a bouncy pirate ship with bubbles, a live tiger, money booth, personalized gift bags, a drumline, and Tom's ex Lucy -- whom Jean-Ralphio invited not for Tom's sake, but for his own, but who kisses Tom, not J-R, before the party is over.
And April and Andy are using the possible end of the world as a reason to cross entries off Andy's bucket list: win the lottery (he wins $10 off a scratch off), hold $1000 cash in his hands (Andy has the teller give it to him in $1 bills), make the most amazing grilled cheese sandwich ever made. And with Jerry and April's sister's help, April and Andy film an action movie where Andy's alter ego FBI Agent Bert Macklin saves April's Janet Snakehole, before deciding they have the momentum do something incredibly stupid before they can realiz how stupid it is, and take off for the Grand Canyon (where April can't even muster annoyance and Andy's confusion about where the giant carved president faces are is short-lived.)
Herb realizes he made some mathematical errors, so the world is in the clear until May 19th, but the park's booked, so the end of the world is moved to May 20th -- which means Leslie and Ben have a little more time to work it out, Tom can find a new job and Andy and April can get home. Plus, Ron can cash all of those checks.