|At this very moment, Leslie is throwing herself in front of a freight train named Tammy for me, and you. Leslie is a wonderful loyal friend who is very important in my life, but I would sooner visit Europe than have something romantic happen between us.|
|— Ron Swanson|
Leslie Knope congratulates Ron Swanson on his award nomination from the Indiana Fine Woodworking Association for a chair he recently constructed. Ron realizes this may be the first time he's ever actually wanted to attend an event, and plans on taking his girlfriend Diane Lewis. Leslie subsequently invites herself.
Now that it's finally December, Tom Haverford, April Ludgate, Andy Dwyer and Donna Meagle are planning their annual, sacred event: the Jerry Dinner. They explain to Ann Perkins that anytime Jerry Gergich does something stupid, they put a dollar in a box. This year, they've collected over $500, which means a fancy dinner. Ann doesn't approve of this sort of mockery, but her opinion is waived off by the group. Meanwhile, Chris Traeger and Ben Wyatt make plans to hang out.
That night, Ron and Diane arrive at the awards ceremony. They immediately run into Leslie, who's overjoyed at finally getting the chance to meet Diane. As a giddy Ron runs off to check out some jackplanes, Leslie eagerly turns on Diane in an attempt to quickly get to know her.
While on their way to dinner, Donna has a change of heart. She turns the car around and drives to Jerry's house to invite him to dinner. However, upon arriving at Jerry's house, they find he is throwing a large-scale Christmas party. The four of them are confused as to why they weren't invited, as they spot Ann, Chris and Ben arriving at the front door. Inside, Chris accidentally indulges in regular, fattening eggnog. Ben fears a breakdown, but Chris is just shocked to find out how much better things taste when there's fat in them.
Back at the awards event, Leslie is head-over-heels excited about how perfect of a fit Ron and Diane are. Though Ron neither wants nor needs her approval, Leslie keeps on giving it and giving it. Just as she's musing about how this just may turn out to be the best night of Ron's life, she hears a familiar voice from across the room: Tammy 2, Ron's ex-wife, has entered the building. Tammy beelines straight for Ron, ever eager to mess with him and potentially ruin his life. Leslie is quick to usher Tammy away and warn her not to mess with Ron's big night. Tammy does not heed to Leslie's warning.
Back at Jerry's, the cold foursome is huddled outside a window, peering in at the warm, lovely festivities going on inside. When they get Ann's attention, Ann ends up letting Donna inside, but keeps the rest of them out. Chris introduces Ben to Jerry's wife Gayle Gergich, but Ben is a little taken back by her beauty. Minutes later, Jerry and his family joyfully perform a Christmas tune for the guests. Outside, Tom and April realize they never received Jerry's invitation due to filtering all of Jerry's emails. Looking through their spam folders, they uncover three years worth of emails from Jerry: wedding congratulations, birthday messages and, of course, their party invitations.
At the ceremony, Tammy plops herself down at Ron's table. When Ron is announced as the winner of the "Achievement in Chairs" category, Tammy distracts him from his heartfelt speech by crossing and uncrossing her legs, flashing him. Later, as Diane and Leslie are both looking for Ron, Diane admits that she's not actually threatened by Tammy. Rather, she's concerned with Leslie. She and Ron have an intimacy that Diane doesn't understand, and if anything is a threat to their relationship, it's Leslie. When Leslie finally finds Ron, she tells him about Diane's misconceptions. While Ron is anything but romantically connected with Leslie, he does finally admit that they're friends. Leslie hands him her car keys so that he can go find Diane, while she goes off to deal with crazy Tammy hiding out in Ron's car.
At the Christmas party, Chris calmly deals with the sudden arrival of his former girlfriend, Millicent Gergich, much to the surprise of Ben, while Ann finally lets April, Andy and Tom in after they hand over the $500 to Jerry as a gesture of good will, under the guise of having raised money for his hospital bills.
Working hard to keep Tammy off Ron's trail, Leslie drives the car to the middle of nowhere and tries to dispose of the keys, but Tammy's too quick for her. They spend the entire night fighting. At a quiet bar, Diane admits to Ron that she's worried that she'll never get as close to him as Leslie is. Ron then shows her something that not many people know about, especially not Leslie: his alter ego Duke Silver.