This episode begins at the Moondance Diner, where Ross, Joey, Phoebe, and Chandler are seated at the counter. Monica is working and is in full costume, which features huge, fake breasts. They are planning Rachel's surprise birthday party and Monica wants it to be fancy. Everyone else wants it to be a low key, pizza and beer type affair. All Joey seems to be interested in is Monica's fake breasts.
Now Chandler, Joey, Ross, Monica, and Phoebe are in Central Perk. They are still planning Rachel's birthday party. We find out that neither of Rachel's sisters can come and that Shannon Cooper "steals stuff" (Joey's way of saying he slept with her and never called her afterwards).
Rachel enters, fresh from her sister's college graduation. She complains about her parents and their inability to get along since the divorce. Luckily, she gets to "serve coffee for the next 8 hours". She heads off to start her shift.
The friends discuss which parent to invite to Rachel's party (Monica already invited Rachel's mom, so the choice is an easy one). They also find out from Joey that Stacy Roth "also steals"
Now in Monica and Rachel's apartment, Monica, Chandler, Joey and Phoebe are getting things ready for the party. Monica reveals that instead of a birthday cake, they will be enjoying some birthday flan. It's a traditional Mexican custard dessert (or to Joey, it's "goo").
A knock on the door turns out to be Mr. Green (Rachel's dad), who is dropping by unannounced for Rachel's birthday. Despite the friends' efforts, Mr. Green knows it's a surprise party.
Another knock on the door turns out to be Rachel's mom. Monica slams the door shut in Mrs. Green's face before Rachel's parents see each other. Joey takes Mr. Green to Rachel's bedroom to put away his coat. Monica opens the door and Mrs. Green enters the apartment. Phoebe takes Mrs. Green to the bathroom and Joey, seeing the coast is clear, brings Mr. Green out of the bedroom. The friends tell him that they are in the staging area and that the party is going to be across the hall, at Chandler and Joey's apartment.
Later, in the hallway between the two apartments, Chandler is ushering people to the parties. He is sending all the attractive women to his party, which Monica takes offense too. Chandler hears Ross and Rachel coming and clears the hallway.
Ross and Rachel talk in the hallway for a minute and then enter Monica's apartment to cries of "surprise". After "happy birthdays" and greetings, Monica takes Ross and Rachel aside and tells them to go across the hall to the other apartment. They leave Mrs. Green's party and get a second "surprise" for Rachel at Mr. Green's party.
It's later at Chandler and Joey's. Rachel, Chandler and Ross are talking about their current situation. Rachel is upset, but looks forward to two birthday cakes. Chandler breaks the news about the flan.
Later, at Chandler and Joey's, Chandler comes running out of the bathroom. He is excited about some girl calling him "Dennis" and sticking her tongue down his throat. Rachel asks Ross to keep her dad busy so she can go to the other party.
Speaking of Monica's party, they seem to be in the beginning stages of some boring party game involving embarrassing memories and the writing of said memories on a sheet of paper. Monica is not the most exciting party host.
Back at Chandler and Joey's, Ross is engaged in some uncomfortable small talk with Mr. Green.
Next, back at Monica's party, Gunther tries to make a quick getaway. Monica catches him and thwarts his attempt. Phoebe tells him that she will make a diversion so he can escape.
Back at Chandler and Joey's, Ross offers to get a Scotch for Mr. Green. He heads over to Monica's party, where the Mrs. Green sees him with the Scotch. She recognizes it as Mr. Green's drink of choice. Ross plays it off and exits Monica's party, only to find Mr. Green in the hallway. He is on his way to get his cigarettes out of his jacket (which is in Rachel's bedroom still). Ross offers to get Mr. Green his cigarettes and glasses, entering Monica's party again and leaving Mr. Green in the hallway.
At this point, Phoebe is distracting Monica so Gunther can make his escape. At the same time, Mrs. Green sees Ross with that glasses and asks him whose they are. Ross puts them on and says they're his. After being grilled by Mrs. Green, Ross exits Monica's party and meets Mr. Green in the hallway.
Mr. Green is getting impatient with Ross, but takes his glasses and cigarettes anyway.
Back at Monica's apartment, Phoebe is arranging to get a few more party guests over to Chandler and Joey's party.
Monica is now at Chandler and Joey's party, asking them to "keep it down". She sees Gunther, who rats out Phoebe. Phoebe tells Monica that these people deserve a night of fun. Monica defends her party and then gets hit in the head with a volleyball.
Back at Monica's, Mrs. Green is accusing Rachel of choosing a boyfriend that is exactly like her father. This is followed by a montage of scenes where Mr. and Mrs. Green complain about each other to Rachel. She is clearly overwhelmed by it all.
Later, Rachel is sitting in the hallway between the two apartments. Chandler exits his party and sits down next to her. They talk about Rachel's childhood and how things were before the divorce. The hug and then Ross enters the hallway. He takes over the hug from Chandler.
Back at Monica's apartment, Monica is seeing her guests off. Mrs. Green says she is leaving and they go out into the hallway where Ross and Rachel are. While Rachel and Mrs. Green are saying their goodbyes, Mr. Green attempts to exit Chandler and Joey's. Ross blocks the door and then holds it closed from the outside.
Inside, Chandler asks Mr. Green where he's going. Mr. Green says he's getting his coat and leaves the apartment again, this time unincumbered by Ross. The guys form a human wall between Mr. and Mrs. Green while he walks from one apartment to the other. The scene ends with Joey kissing Mrs. Green passionately to distract her, while Mr. Green leaves Monica's apartment and goes down the stairs. Mrs. Green tells Joey that this is the best party she's been to in years. This pleases Monica greatly.
The episode ends with a close up on the birthday flan. The friends all talk off camera about the flan and what it looks like. Rachel makes her birthday wish and blows out the candles. Someone calls "heads up" and a volleyball lands in the flan.
Rachel: Wow, those things almost never come true.