Chris storms into Cagney's, where Nick and Gary are already sharing a couple of beers, a twin on each of their laps. Holding up an invitation, Chris explains that not only has Sheila organized Ernie's first birthday party without any input from him, but she's also ordered him to write a poem for the occasion! And it gets worse: there's going to be a string quartet, a pinata full of raisins, AND Kareem Abdul-Jabbar, Sheila's boyfriend. The guys convince Chris to take advantage of being divorced and thrown his own party for Ernie, as he sees fit. Chris happily agrees.
Later that night, as Marny and Gary are cleaning up after dinner, Marny chastises Gary for eating a chicken nugget directly from the floor. Gary doesn't understand the fuss. Sure, he sometimes eats stray goldfish from the bottom of the diaper bag, but many times he's witnessed Marny eating from food in the sink! They both pause a moment, shocked at who they've become. Marny points to the large photo that hangs in the dining room: a black and white shot of them in full wedding regalia, jumping for joy. Can they even still jump like that? Gary and Marny grab hands and try to leap, neither of them getting much air. A determined Marny puts her foot down. What they need is a detox!
The following day, Chris sends out his evites. Emily's confused as to why Chris has invited Sheila, but Chris assures her that Sheila will be busy antiquing with Kareem that weekend. For a moment, he reminisces about the good ol' days, when he saw Sheila as everything he'd ever wanted: gorgeous, smart, challenging. On cue, Sheila strolls into the apartment to ask Chris about the evite she just received. At first, she's upset that she can't make it that weekend, but she quickly recovers, musing that it's okay if she misses Ernie's unofficial birthday party. After all, it's not on his real birthday, so she gives Chris her blessing. Chris is about to lose it. Before matters escalate, Emily escorts Sheila out the door.
A cheerful Gary pours a mucky green substance into a cup and hands it to Marny, who crinkles her nose in disgust. It's the start of their six-day kale diet - and Marny's already trying to get out of it. Maybe all they need for more energy is a good night's sleep! Gary explains: the twins have sworn to kill them through exhaustion - sleep is a thing of the past. Fighting their gag reflexes, the couple downs the concoction in one foul gulp. After all, if they survived that Habitat for Humanity vacation Gary planned (the one where he thought they would get to keep the house in the end), they can make it through this! When Clark and Yoda leave their plates on the counter and head back to their rooms, Marny eyes the left over tater tots longingly. Gary, fearing a breakdown, springs to action and sprays the spuds with counter-top cleaner.
It's the day of Ernie's "unofficial" birthday party, and Chris' apartment is certainly set for the occasion: blue slushies for the kids and booze slushies for the adults. There's a station for temporary tattoos, where little Violet is getting a skull with a snake coming out of its eye. Chris even made a cake, which, in reality, is merely a sad looking chocolate lump with some sparse icing. As Gary and Marny arrive at the party with the kids, Nick offers them each a beer, but they proudly refuse. Gary pulls out an enormous bag of kale; it's all they need! Chris gets an unexpected surprise when Sheila walks through the door; Kareem's dumped her. But it's for the best, or so Sheila claims. She should be here for Ernie. The first thing she does is take away Ernie's lollipop (choking hazard!) and the next is to insult Chris' cake with a "Great Expectations" reference that no one else seems to get. Guess the party's really starting now...
Gary, Nick and Chris, along with Fred and Ernie, are seated around a makeshift blackjack table. A determined Fred taps the table with a "hit me" gesture, and Nick deals him another card. Sheila comes over to the table and tells Chris that she really doesn't want Ernie getting one of those tattoos. Chris, mocking concern, lifts up Ernie's shirt to reveal what's already there: a temporary "Thug Life" tattoo over Ernie's belly. As Sheila scoops Ernie out of Chris' arms, Nick begs for Chris to kick her out. Chris is reluctant; he doesn't want one of their famous party-ruining fights to torpedo Ernie's day. Nick suggests that someone should go on full-time Sheila duty. After a quick round of high card, Emily gets the dirty duty.
As the guys play "who falls first" with their young tots (for money, no less), Sheila has gathered the ladies at the party, so she could talk about her breakup with Kareem. She's interrupted by the doorbell, which turns out to be a cake delivery. Chris can't believe it: even though he baked, Sheila went ahead and ordered her own dessert for Ernie, a gorgeous vanilla cake lined with lavender frosting. It puts Chris' baking effort to shame. When Sheila goes downstairs to grab a cake plate, Chris can barely hold it together. She's ruining everything! Nick pipes in with a suggestion that'll get her out of the apartment: they can text Kareem from Sheila's phone, apologizing for being overbearing and asking him to come pick her up. Meanwhile, Gary and Marny are hovering over the cake, their hands shaking for anything that isn't another bite of kale. Gary comes close to tasting the frosting, but heroically holds himself back. They've only got two days left on this kale diet from hell!
Later, Sheila's seated on the couch, once more lamenting about Kareem, and how being alone is not the same thing as being lonely. Chewing on a piece of kale, Gary strolls over to Sheila and asks to try on her purse, claiming he's thinking of getting Marny the same one. As he swings it around, Chris crawls behind the couch and secretly grabs Sheila's phone from the bag. He quickly throws it to Nick, who walks out the door with it, Emily in tow. Nonchalantly, Gary gives Sheila back her bag. In the hallway, as Nick and Emily try to craft the perfect text message to Kareem, Sheila's phone begins to ring. Seeing that its Chris' number calling, Nick picks up, only to find Sheila on the other end. Sheila meets them in the hallway, demanding to know what they're doing with her phone. Emily admits that Chris doesn't want Sheila at the party, since it's hard for him to see her. Sheila misreads this completely and thinks that Chris is lonely and misses her. She seems touched. Nick and Emily don't correct her, since she agrees to leave after the cake is served.
Gathered around Ernie, all the party guests sing "Happy Birthday" as Sheila and Chris help Ernie blow out the candle on Chris' homemade cake. As Emily tries to snap a family photo, Sheila admits to Chris that Emily and Nick told her how he feels, and she apologizes. She asks Chris why he didn't just tell her himself, and Chris, thinking that Sheila finally understands that he doesn't want her around because she drives him nuts, admits that he wasn't sure how she'd react. As the two move closer for the photo, Sheila leans in for a kiss. The guests are horrified, and a terrified Nick stops the madness by spraying the couple with whipped cream.
As they're cleaning up, Chris cannot figure out Sheila's intentions. Why on earth did she kiss him? What gave her the crazy idea that he misses her? Sheila, red with embarrassment, tries to play the kiss off as a joke. Just as she gets up to leave, Sheila takes the cake she ordered and hurls it at the wall, shattering Chris' grandmother's cake plate just like she did the punch bowl at Ernie's christening. Later, when Nick is taking out the garbage, he catches Sheila crying in the trash room and though he can barely stand it, he offers Sheila a napkin. He takes his cue to leave, but Sheila starts venting. A child's first birthday party is supposed to be a celebration for the parents as well, showing them they've made it. But she and Chris haven't made it. Wiping a tear from her eye, Sheila admits that she feels like she's failed as a mother.
In true Nick fashion, Nick admits that though she may have failed as a human being, she's a great mom. At that moment, Kareem Abdul-Jabbar opens the door to the garbage room. He received Sheila's text, and if she's serious about being sorry, then so is he. The two embrace as an awestruck Nick watches. Moments later, Sheila returns to Chris' to pick up her purse. Smoothing things over, Chris and Sheila realize that even though they're not together, Ernie will always connect them. There shouldn't be two of this or two of that; they should all celebrate things together, as a family. Later, Gary sits in his apartment, eyeing the remains of the cake. Marny begs for their crazy diet to end. Who are they starving themselves for? They'll never be the Gary and Marny in their wedding photo, and that's because that Gary and Marny didn't have four kids! Gary agrees and tells Marny that she's just as fun and as beautiful as she was on the day of their wedding. Gleefully, they each scoop up a handful of cake and begin feeding each other, overjoyed.