Dee Dee attempts to get closer to Mona by planning a joint birthday party, reminding Mona of bad memories from their childhood. Meanwhile, Dee Dee unwittingly reveals that Phyllis lied to Mona about things that have shaped her world view since she was young; and, as a birthday gift, Phyllis finally tells Mona the truth.

Dee Dee persuades Mona to attend a banquet that's being held in honor of their father, but the experience reminds Mona that she's the odd one out within her dad's ""new"" family.

The gals' already tenuous friendship spirals toward dissolution when Dee Dee celebrates the end of her school year by hosting a raucous celebration that keeps Mona awake all night. Things get worse when Dee Dee installs a hot tub, which floods Mona's apartment. Stepping in to mediate, their father, Charles, reminds them that ""like it or not, we're family."" But the squabbling continues, until a medical emergency involving their dad arises.

After Dee Dee loses her old room to the baby and Big Dee Dee misses several appointments, Dee Dee begins to worry that the baby is forcing her out of her parents' life. She suffers from so much stress that she has a breakdown and hears a doll talking to her. Mona recommends that she make an appointment with Phyllis to discuss her problem. She says that she feels as though she is the only one who is worried about the way the baby will change her life. Phyllis assures her that her reaction is perfectly natural and that she should air her concerns with Big Dee Dee. Before she gets around to it, Big Dee Dee admits to her own anxieties about the child's birth, and thanks Dee Dee for her support. The conversation reassures Dee Dee about her importance in her mother's life. Meanwhile, Spencer continually cancels on Mona because of plans with Camille. She looks to Adam to take his place, but Adam isn't too thrilled about this.

Hoping to prove herself to her father, Dee Dee goes against his wishes and tries to personally handle a tenant who has failed to pay rent for the last few months. She must come up with a new plan of attack after the man retaliates by threatening to expose several building code violations involving Dee Dee's apartment. Meanwhile, Mona reluctantly takes her mother out on the town. She feels crowded when Phyllis begins showing up regularly at her hangout and playing matchmaker for the patrons.

Dee Dee organizes a singles mixer at a local club. She bristles at Mona's claim that she only dates a certain type of man (well-groomed and upwardly mobile), and tries to prove her wrong by picking up a tough guy named Keno. She takes off with him on his motorcycle and joins him at a bar, where she rides a mechanical bull. She has a good time exploring this new side of herself--until she runs into a very angry woman who claims to be Keno's girlfriend. Mona and Nick crash the mixer and meet up with his ex-girlfriend, Raquel. Mona is disturbed to discover that Raquel is her dead ringer, and fears that Nick is just with her because of the resemblance. Meanwhile, Dee Dee must actually care for Drew herself after firing the nanny. She is mortified when she must turn to Phyllis for help when her son will not stop crying.

Mona returns from a Hawaiian vacation and clears the air with Spencer. They reaffirm their decision to just be friends. While looking through some vacation photos with her family, Mona reveals that she can now ride a horse. She is stunned to learn that Dee Dee still has the horse their father gave her as a child, Daddy's Favorite, and that she has lied for years about having not kept the horse. (The horse led to a major rift between Charles and Phyllis that separated the sisters for a decade.) Mona decides to buy her own horse, but it doesn't quite go as planned. Meanwhile, Adam helps Spencer uncover the cause of Kai's sudden unpleasant attitude toward him.

After Dee Dee bests her at an online word game, Mona grows frustrated by the fact that she always loses to her sister. She becomes determined to beat her at something, and sees her opportunity when Dee Dee organizes a poker party for one of her law school professors. Their mothers decide to crash the event, where Phyllis winds up winning Big Dee Dee's wedding ring in the pot. Meanwhile, Adam tries to get access to a copy of Spencer's personal music playlist.

After throwing together a baby shower for Neil and Janet, Dee Dee becomes concerned by the fact that she is the only person in attendance who is not attached. She begins to question her life and decision to pursue her career so aggressively. Meanwhile, Mona worries that her lack of maternal instinct could have a negative effect on her relationship with Chase. She tries spending time with Drew, and receives some advice from Big Dee Dee.