Don has to look after Sally and Bobby after Pauline breaks her ankle tripping over the telephone cord. He's also hosting Megan's parents, Emile and Marie. Emile, a socialist academic, makes his dislike of Don clear. Megan confides in Don that her parents are arguing because Emile is cheating on Marie with one of his students. At dinner, Megan serves Sally spaghetti, just like her mother served her as a child.
Roger meets his ex-wife, Mona, for drinks. He tells her about his recent LSD experience and asks for her help in arranging meetings with potential clients who he will be encountering at the upcoming American Cancer Society dinner, at which Don will be given an award for that letter. Mona, who knows that Roger and Jane are going to divorce, agrees to help him.
Inspired by having dinner with her parents and Don's children, Megan has an idea for the Heinz campaign — a mother serving her child beans in various historical contexts, from caveman times through to the future. They discuss different tag lines, and an excited Don tells Stan and Ginsberg about the idea. Both complain about the last-minute change of plan but admit that it's better than anything else they've come up with.
Abe calls Peggy and insists on meeting her for dinner. Thinking he's going to break up with her, Peggy confides in Joan, who suggests that he might actually be going to propose. Peggy therefore gets a new dress for the dinner, but Abe actually asks if she'd like to move in with him. She hesitates before saying "Yes". When she tells Joan about this the following day, the latter calls it a romantic notion and suggests that, from her own experience, marriage may be overrated.
At dinner with Raymond from Heinz, Megan learns from Raymond's wife Alice that Raymond is planning to fire the agency. After informing Don of this, she improvises a segue which allows him to pitch Megan's idea — which Raymond loves. At the office the following morning, everyone praises Megan, although Peggy tells her that "this is as good as this job gets".
Peggy and Abe have her mother round for dinner. She makes her disapproval of their cohabitation very clear. Not because Abe's Jewish, but because she disapproves of "living in sin" and thinks he's using Peggy for "practice" prior to marrying someone else.
Sally asks if she can go with her father (and Megan and her parents) to the ACS dinner. Don agrees, but after she gets dressed for it he tells her to ditch the make-up and the go-go boots. At the dinner, Roger — who immediately gets on well with Marie — makes a fuss of Sally, telling her about all of the other attendees. Pete introduces Don to Ed Baxter (Ray Wise), Ken's father-in-law) who tells Don that the companies represented at the event love his talent and will give him awards but, because of the letter, they'll never hire him. Emile tells Megan that she has changed — her marriage to Don has allowed her to take a shortcut in life instead of working for it, reminding her of her acting dreams she was once so driven about. She rebuffs him, but is visibly bothered by this truth. Looking for the toilet, Sally accidentally walks in on Marie fellating Roger. The dinner ends with Emile, Marie, Megan, Don and Sally sitting at their table, all looking discouraged and discontented from what's happened.
Back at Don's apartment while everyone is sleeping, Sally calls Glen. He asks her how the city was, and she replies that it's "dirty".
Tropes Appearing In "At the Codfish Ball":
- Actually Pretty Funny: At the ACS dinner, when Emile asks Pete what he does, Pete replies by asking about Emile's work, and how important he's heard Emile is at the university — inflating his ego and kissing his ass, in short. He ends with, "That is what I do." Emile chuckles at this.
- Amicable Exes: Roger and Mona are depicted on much better speaking terms, having drinks and talking about his recent experience with LSD. He even asks her to help arrange meetings with potential clients, which she obliges.
- Brain Bleach: What Sally could do with after inadvertently walking in on Marie fellating Roger.
- Continuity Nod: Don asks Ed Baxter to introduce him to some potential clients during the American Cancer Society award ceremony but Ed declines, explaining that while the clients like his work, they don't like him because of that letter he wrote.
- Cool Uncle: Roger, to Sally. He's one of very few adults who treats her like a grown-up, and they get on well as a result. Although this effect is rather spoilt when Sally walks in on him and Marie...
- Dating What Daddy Hates: Megan's father, Emile, is a socialist and hates Don because of his job. He doesn't shy from expressing his disapproval to Megan later on, saying that marrying Don forced her to abandon her dreams of becoming an actress.
- "Eureka!" Moment: Megan cracks the season-long Heinz problem just in time with a campaign of a mother serving her child beans in various historical contexts, from caveman times through to the future, after having serving spaghetti to Sally and Bobby the night before, and remembering her own mother serving her spaghetti.
- Fake Ultimate Hero: Sally caused Pauline to break her ankle — she tripped on the phone wire because Sally had taken the phone to her room — but after she tells Don that Pauline tripped on one of Gene's toys, he praises Sally for her quick thinking in dialing 911 and making sure Pauline was comfortable until the ambulance arrived.
- Freudian Slip: After seeing Sally dressed up for dinner in a very Megan-esque outfit...Emile: There is nothing you can do, Don. One day your daughter will spread her legs and fly away.Megan: Wings, Daddy. You mean wings.
- Friendship Moment: Joan being sincerely happy for Peggy when she reveals her and Abe's Relationship Upgrade.
- A little later, Peggy is sincerely happy for Megan when she hears Megan came up with the idea to land the Heinz account.
- Foreshadowing: The attraction between Marie and Roger is instantaneous and mutual.
- Glory Hound: Harry tries to claim some of the credit for the Heinz pitch even though he wasn't at the dinner. Ken, who was, calls him out on this.
- Mama Didn't Raise No Criminal: Mrs. Olson would rather her daughter lie to her than tell her that she is "living in sin".
- Oh, Crap!: Two in rapid succession during the dinner with Raymond Geiger of Heinz:
- Alice not so subtly tells Megan that Heinz will be firing SCDP while they're in the bathroom.
- Megan returns from the bathroom and whispers to Don's ear that they're being fired.
- Passive-Aggressive Kombat: Emile convinces Bobby to refill his fountain pens on Don's white carpet.
- Pet the Dog: Roger doting on Sally at the ball; he and the debutante even engage in some Snark-to-Snark Combat. Marie is certainly endeared.
- Relationship Upgrade: Abe and Peggy move in together.
- Rule of Symbolism: During the American Cancer Society award ceremony, Roger orders Sally a Shirley Temple, which is supposed to be a symbol of "a child trying to be an adult". After Sally witnesses Marie fellating Roger, she tells the server she's finished with the Shirley Temple, showing how she has had adulthood forced upon her.
- Shout-Out: Don's reading The Fixer by Bernard Malamud. Contrary to what Megan assumes (probably from her knowledge of his reading habits), it's not a James Bond novel.
- So Proud of You: A touching father-daughter moment at the dinner, where Don tells Sally that she's a beautiful girl who will one day wear make-up, but not tonight.
