Knowing Leni's history of spoiling surprises, the children decide not to tell her about their mother's upcoming party.
The siblings are holding a meeting, but Leni isn't present, due to Cliff distracting her. The siblings are discussing Rita's upcoming surprise party, and Lincoln explains to the viewers that the reason why Leni isn't present is because she's notorious for spoiling surprise parties. After Lori gives a rundown of what each family member's task is (Lori will clean up, Lola and Lynn will make food, Lana and Lucy will decorate, Luna and Luan will provide entertainment, Lisa will handle the guest list, and Lynn Sr. will take Rita out of the house), she informs Lincoln that he has the most important task: keeping Leni occupied while everyone gets the party ready. Without warning, Leni enters the room, and Lincoln tricks Leni into asking him "urgent" fashion questions, while their remaining family members sneak out.
When Lynn Sr. takes a clueless Rita out to go shopping, the sisters get to work prepping everything up. However, when Leni decides to go downstairs to get something to drink the sisters quickly try to hide their decorations so Leni doesn't see them, with Lincoln unable to warn his sisters in time due to forgetting their code phrase for Leni. After having shown Lincoln every type of fabric and pattern, Leni prepares to gossip with Cliff, but Lincoln once again distracts her by letting her use him as a model. In the hallway, Luna and Luan attempt to bring their entertainment equipment downstairs without making too much noise, however, Luna trips on a set of wind-up teeth, causing her to drop her drums, catching Leni's attention. Lincoln tries to warn Luna and Luan about Leni, but in the process, accidentally falls down the stairs. When Leni checks up on Lincoln, Lincoln comes up with a way to fully distract Leni: go to the Hazeltucky Party Outlet to get a scratch-and-sniff card that features a camel wearing a spacesuit that says "Happy Birthday from your 11 kids!" Falling for the trick, Leni leaves, thus giving the remaining siblings enough time to set up for the party.
As the siblings prep things up, they soon realize that the party is disastrous because Lana has to resort to using chewed up gum as an alternative for balloons, Lucy has to use toilet paper when she runs out of streamers, Lisa has invited Flip, Mr. Grouse, and Dr. Feinstein, saying they're the ones who Rita frequently interacts with, Luan's jokes revolve around her making fun of their mom's age, Luna's rocking music is ear-grating, Lola's cake is too sweet, and Lynn's subs are too spicy to handle. As the siblings begin to ponder what they did wrong, they realize that they need Leni, because despite her spoiling the surprise, she actually knows each of her family member's interests. Lori tries to call Leni on her phone, but Leni mistakes her ringtone as music coming from the selection of birthday cards present. Because of this, the siblings proceed to look for their sister themselves.
Several hours later, the siblings, who were unsuccessful at finding Leni, arrive back home. Upon entering, they discover that the entire living room is decorated, and there's a more refined guest list, such as Albert, Pam, Ruth, and a brunette woman. It turns out that Leni arrived back home while they were away, and thought even if they were going low-key with their Mom's party, she wanted to decorate away (she even managed to get the card that Lincoln requested). Suddenly, Rita and Lynn Sr. arrive back, prompting everyone to find a hiding spot. Upon entering, the guests shout out "SURPRISE!", and Rita is happy about everyone's hard work. The siblings apologize to Leni for leaving her out and decide to make her the family’s official party planner, however, Leni ultimately spoils an upcoming surprise party for Lynn Sr., causing her family and the guests to facepalm out of exasperation.
Pam was not originally in Jordan Koch's storyboard for this episode, and was added later on.
This episode reveals that Lana keeps a stash of chewed up ABC gum underneath the stair banister.
This is the second episode to have Lori's hair stylized in a ponytail, the first being "Garage Banned".
This is the second time Lynn Sr. is joining the family meeting, the first time happened in "Study Muffin".
In the Latin American dub of the series, when Leni spoils Luna about her party, Luna doesn't say "Dude", she says "Leni" instead. Indeed since "dude" doesn't have a direct Spanish translation.
In the dub, Flip isn't voiced by José Antonio Macías.
Irony: The siblings tried to keep Leni away so she wouldn't spoil the surprise party, but she ended up having the most knowledge on Rita's personal interests.
Karma: Flip wanted to give an expired milk as a present, but he ended up drinking it himself.
Moral: The odd one out might have the best information.
No Spoilers - The title relates to someone watching a TV show, movie, or playing a video game, without any spoilers, because that person hasn't seen any of it, while others already have.
Foster's Home for Imaginary Friends - The premise of this episode is similar to the Foster's episode "The Big Cheese", since both episodes involve a group of characters trying to accomplish a specific task, but the person they're trying to keep away ends up having the solution to their problems.
Coincidentally, Chris Savino previously worked on that show.
LazyTown - Lola's cake is similar to the cake the characters made in the episode Swiped Sweets.
Peanuts - A shirt that heavily resembles Charlie Brown's can be seen in the pile of clothes that Leni has on her bed.
Kamen Rider Faiz - Lola running super fast for a short amount of time after eating a piece of cake similar to the main character, Kamen Rider Faiz/Takumi Inui, running for up to 10 seconds after his Accel Form became complete.
Power Rangers Lost Galaxy - Lincoln requests that the code word be changed to quasar, which is the name of the Galaxy Rangers main weapons.
When Lola has a brief sugar rush after tasting her cake, her eyelashes are disconnected from her eyes.
When Lori tells Luna and Luan to keep the noise down, she walks through the wall instead of the door.
As Leni walks out of her room to hear what the cymbal noise is out in the hallway, she has a sewing pin in her mouth, but in the next shot, it's gone.
As everyone says "Surprise!", Albert's sideburns are missing.
When Flip arrives at the party, he leaves the expired milk by the door and walks to the sofa, but a few moments later, after eating the submarine sandwich with too much hot sauce on it, the milk teleports to nearby the coffee table so he can douse the heat with the milk.
When Leni goes to the Hazeltucky Party Outlet, she exits the house through the dining room, but there isn't a door to exit the house in that room.
Every time Lincoln smiles when he is with Leni, his chipped tooth is missing.
Lincoln trying to keep Leni distracted.
Lincoln shouting the code word ("daffodil").
The sisters reminding Leni that they're trying to keep Mom's party "low-key".
The sisters hiding their decorations whenever Leni appears.
Whenever the siblings scream, Leni thinks it’s a new way to say hello.
Road Tripped • White Hare/Insta-gran • Roadie to Nowhere/A Fridge Too Far • Selfie Improvement/No Place Like Homeschool • City Slickers/Fool Me Twice • Net Gains/Pipe Dreams • Fandom Pains/Teacher's Union • Rita Her Heights/The Mad Scientist • Head Poet's Anxiety/Missed Connection • Friendzy/Deal Me Out • Pasture Bedtime/Shop Girl • Gown and Out/Breaking Dad • Ruthless People/What Wood Lincoln Do • Scales of Justice/Crimes of Fashion • Absent Minded/Be Stella My Heart • Sitting Bull/The Spies Who Love Me • Really Loud Music • House of Lies/Game Boys • Everybody Loves Leni/Lesson Plan • Udder Terror/Tea Tale Heart