It's a hard-knock life for Lily Samson, who comes from the weirdest family of all time. For one thing, she lives alone with her mom—her dad left before she was born, and her brother, Lonnie, moved out (more on this later). Because her mom works long hours as a psychologist at an adult day care center, it falls to Lily to clean, cook, and do basically every domestic housekeeping job you can think of. On top of that, her mom has a really annoying habit of bringing home elderly people from the center to chill with them for the weekend.
What else? Lonnie and her grandfather, Stan, whom she calls Pop, aren't speaking to each other because Pop threatened him with an ax after Lonnie changed his major for about the fiftieth time. As a result of this confrontation, Lonnie moved to a boarding house near his university, Lily hasn't seen him in months, and her mom spends way too much worrying about him when he's a big boy and can take care of himself. Her grandmother, Nan, also has an imaginary friend named Sef and Lily thinks she might be losing her marbles.
Nan may have a few rolling around on the floor, but she does know two things. First, Sef technically isn't an imaginary friend because as a child in an orphanage, she actually did have a friend named Sef. They got separated when Sef was suddenly adopted.
Second, she knows that something has to be done to get the family back together after The Great Lonnie and Pop Schism. Since her husband is about to turn eighty, Nan decides to throw him a birthday party. Not only will the family get to celebrate, but the conflict between him and her grandson will finally be resolved.
Over at Mercer College, Lonnie is studying English and is obsessed with 19th-century novelist Emily Brontë to the point of having a creepy crush on her. He eventually has the opportunity, though, to have a crush on a real live girl when he meets Clara, a student in one of his lit classes. Clara's family has also written her off—her dad disapproved of her choice of focus for her senior thesis, so she left home, and he no longer considers her his daughter. Okay. That's kind of an extreme reaction to a thesis topic. But still, it gives Clara and Lonnie something they can identify with in each other.
After an awkward lunch with her girlfriends at school where she feels left of out of discussions about fashion, boys, and appearances, Lily decides that her position at home is making her age too fast. In her mind, there's only one solution to this problem: She has to fall in love.
Her victim? Junior class thespian and all-around stud, Daniel Steadman. From hanging around the junior class lounge to joining the school production of Hamlet as a prompter, Lily is determined to get Mr. Hottie to notice her. Still, she feels that her bizarre family, her responsibilities of cooking and cleaning at home, and her short, stocky appearance will keep him from being interested.
On a trip to visit his old neighborhood, Pop has a chance meeting with Clara's mother, Rose, who grew up in the same neighborhood years after him. After initially being irritated with Pop due to an insensitive remark about her race, the two quickly bond over their prodigal children. Rose really wants to go see her daughter's dorm room, but has been afraid of overstepping boundaries. Pop, however, tells her she should go, because as Clara's mother, it's still "her right."
As Nan's party preparations get underway, Lily becomes more and more determined to get Pop and Lonnie to make up. Lonnie's relationship with Clara escalates to the point of getting engaged, and he is afraid that because of Pop's racist tendencies, Pop will reject her, and by extension, him. Because Lily won't shut up about wanting the party to be a beautiful, perfect day, though, Lonnie finally goes to Pop's house—while Pop is out. Still feeling like he didn't do anything worthy of apologizing for, Lonnie tells Nan to tell Pop he's sorry Pop's old dog died.
While Lily doesn't consider this apology fitting, it's just what Pop needs to reconsider his feelings toward Lonnie. He also puts the pieces together and realizes that Rose is Clara's mother, giving him time to reconcile his feelings about race with Lonnie' choice of a mate. When Lonnie and Clara arrive by train to his grandparents', Pop meets them at the station and even kisses Clara on the cheek.
Lily and her mother also get some surprises the day they leave for the party. In spite of Lily's objections, her mother has agreed to bring one of the elderly women from the daycare, Mrs. Nightingale, to the party for the weekend. She introduces herself to Lily as Sef—Nan's old friend from long ago. On the way, Lily stops to mail some letters for her mom, and ends up having a run-in with Daniel. The two make a date to go out for coffee.
All in all, despite the obstacles, family feuds, and generational conflicts, Lily's family is about to get the whole, perfect day Lily's been dreaming about. They toast Lonnie and Clara's engagement, and Nan and Sef even dance in the backyard like they did when they were little girls. But there's one surprise left: The phone at her grandparents rings with a call from Lily's father. She answers the phone and says hello to him.