The episode begins with Little Bill drawing a picture of April playing basketball, pretending that she plays a game and has just won the game for the team. Little Bill shows the drawing to Alice the Great, who says that it looks very nice. He then asks her if April's basketball team won today, but she says that they won't know until April gets home. As Little Bill notes that the team always wins, the door opens and Alice the Great says that April has just come home. Then she and Little Bill walk out to show April the picture he drew of her winning the basketball game, but April doesn't look happy and walks upstairs without talking to them. Little Bill asks Brenda what's wrong with April, and Brenda tells him that April is upset because her team lost the basketball game. Little Bill is sad to hear that they lost; Brenda says that April missed an important shot, feeling awful about it. Little Bill notes that April is the best basketball player in the world. Big Bill says that the drawing is wonderful and tells Little Bill that April will want it when she's all better. Brenda suggests that he save it for her, but Little Bill says that he's going to cheer April up anyway.
Next, he walks into April's room to see her laying on the bed and tells her that he brought her something to cheer her up. However, she tells him that she doesn't want the picture. Little Bill is sad that she doesn't want the picture; April also states that she doesn't want to have anything to do with basketball anymore. Little Bill can't believe what she's saying, and April asks him not to even say the word basketball again. Little Bill tells April that he wants to cheer her up, but she doesn't think anything could cheer her up. Little Bill still thinks he can and starts to do a dance for April saying that she is the best at basketball, but then realizes that he said basketball, making April tell Little Bill to go away , which Little Bill agrees on.
As Little Bill leaves, April takes her trashcan outside of her room and throws away her basketball and her trophy. Little Bill tries to talk with her, but Bobby tells him that he wouldn't do that if he was him. Little Bill gives up and goes into Bobby's room, where he asks him why April would throw out her basketball and trophy. Bobby agrees that this is a bad sign, and Little Bill also notes about how April said that nothing would be able to cheer her up. He asks Bobby if April is mad at him, but Bobby doesn't think so and says that April is only mad at herself. He then notes that April really wanted to win that game and tells Little Bill that the best thing they can do for April right now is leave her alone. Little Bill asks Bobby if April will stay like that forever, but Bobby promises his little brother that she won't. Little Bill is determined to make April feel better, but Bobby warns him not to tell him that he didn't warn him.
As Little Bill walks back to April's room, Alice the Great sees him and tells him to come into her room, noting that he won't do April any good by just staring at her door. Little Bill shows Alice the Great that April threw away her basketball and her trophy. He also notes that April doesn't want to hear the word, basketball, in the house. Alice the Great claims that April is very sad right now, but Little Bill still wishes that he could make her happy again. Alice the Great asks Little Bill about the things that make him happy, and he says that he likes birthdays. He notes that on his birthdays he gets presents, ice cream, and cake, then imagines that it's his birthday, where he's surrounded by presents and a cake. He opens up a gift and inside is April's trophy, which makes him cheer. Little Bill is snapped out of his imagination by Alice the Great telling him to be careful with April's trophy. Little Bill says that they should throw April a birthday party, but Alice the Great disagrees that it isn't April's birthday yet, so Little Bill says that they should throw her a not-birthday party. Alice the Great laughs and agrees that it's a wonderful idea.
Little Bill runs into Bobby's room and tells him that they are going to have a not-birthday party for April. Bobby is confused, so Little Bill explains that it's a party that will hopefully cheer April up, also adding that it's a surprise. Bobby doesn't think it makes any sense, but Little Bill insists that it'll be fun and Bobby can help him. Bobby agrees to help out. Then he and Little Bill sneak past April's door and go downstairs. In the kitchen, they tell their parents about the not-birthday party. Big Bill and Brenda are confused, so Little Bill says that they should get not-birthday gifts, cake, and ice cream. Big Bill thinks he'll make pizza for dinner tonight because it's April's favorite; Little Bill also tells him to put pineapple on it. Big Bill thinks that's a good idea, and Little Bill notes that April loves pineapple on her pizza and asks if Big Bill can make it tonight. Big Bill agrees, and everyone is happy. Little Bill asks Brenda if they can put birthday candles on it. Brenda says that she has some leftover ones, which Little Bill thinks they should put them on the pizza like a birthday cake. Then Bobby asks about decorations, and Brenda says that they have decorations in the party box. As Big Bill asks for Bobby's help with the pizza dough, Little Bill thinks about what he can get as a not-birthday present for April.
That evening, Little Bill walks into April's room, where she replies that she wants to be alone. Little Bill tells her that it's dinner time, but she asks him to tell everyone that she's not hungry, so he knocks again and runs downstairs. April comes out and Little Bill starts to laugh, making her ask him what he's doing. Little Bill laughs again and runs down the stairs, which makes April tell him to quit being weird and follow him down the stairs. Little Bill peeks around the corner and laughs again, causing April to yell again that he's being weird. She then notices that everyone is missing, so she walks outside to find balloons, party decorations, the pizza, and everyone outside, where they wish her a happy not-birthday. April comes out and everyone starts to sing. Then she laughs and notes that Little Bill tricked her. Little Bill tells April to blow out the candles, which she does and makes everyone clap. Big Bill asks April if she's ready for her presents. April can't believe that there are presents, so Little Bill pulls out a present, which April knows what it is: her trophy! She thanks Little Bill for not throwing it away, and he gives her another present: her basketball, noting that April said basketball. April thanks everyone and asks them why they're having the party, noting that she still lost the game. Brenda tells April that they will always be proud of her no matter what and Big Bill adds that she'll always be a champion to them. Alice the Great also tells her that Little Bill wanted to do something special for her. Bobby notes again that he wanted to cheer her up, and Little Bill asks her if she is. April says so and kisses Little Bill on the cheek. Big Bill asks everyone if they want to eat some pizza, which everyone agrees on, ending the episode.
Later that night, Little Bill holds April's basketball, noting that she let him borrow it. Little Bill says that the basketball is important to April, adding that some things that is important to him are elephants, hamsters, going to the park, birthdays, and many other things. He asks us if we've ever had a not-birthday party before, then starts to sing the Happy Not-Birthday song. Alice the Great calls into the room and asks Little Bill who he's talking to, but he simply chuckles and plays with the basketball during the closing credits.