With Luan locked in a cell in the basement, who is responsible for the April Fool's Day pranks this year?
Lincoln is hard at work patrolling the door the basement. He explains to the viewers that today is April 1st, also known as April Fools Day; the day Luan becomes a crazed maniac by relentlessly pranking her family. Wanting to ensure that she does not pull any pranks whatsoever, the family have gone the extra mile by securing Luan in a locked cellar in the basement a week beforehand. Going into the basement, Luan tells Lincoln that she has retired from April Fools pranks, saying she has grown up now. However, Lincoln refuses to listen, and after a petrified Lynn Sr. comes down with her lunch, Lincoln prepares to head back up. Suddenly, a salami on a string comes down and swings right into Lincoln's face. Lincoln accuses Luan of setting that up, but Luan tells him she did not do that because she is locked up. Suddenly, the house vibrates, and when Lincoln goes to check it out, he sees his family being mercilessly pranked by booby traps set all over the house. The family attempts to seek refuge in Lisa's underground bunker and the garage, but they too have been laced with pranks.
The family goes to confront Luan to tell her to stop with her pranks, but Luan tells them she is innocent, saying she retired from April Fools pranks. However, the family thinks she is lying and prepare to leave, but Lincoln realizes that the pranks that hit them are much different from Luan's usual ones, like how some of the materials that were used were only done during a specific time of their lives. Despite this detail, the family refuses to listen, and leave when Lincoln suggests letting Luan help them catch the real prankster. When Luan says she knows how a prankster would think, Lincoln decides to let her out under certain conditions.
After carrying Luan, wearing Lynn's hockey mask and tied to a dolly with Lynn's sweatbands, upstairs, they enter the bathroom, and discover that no one has entered yet. After agreeing to let Luan loose, Luan observes that the toilet was set to explode the next time it flushed, and that there is a tripwire connected to a tarp full of eggs. She also realizes that whoever set them haven't left any clues of their presence. Meanwhile, the rest of family is on a drive to get away from the madness, and decide to get something to eat at Burpin' Burger.
Arriving downstairs, Luan tells Lincoln to look at the couch. He sees Charles sipping a box of juice, and thinks it normal. Approaching the dog, Luan tells him to come down, when he suddenly responds with "No!" and can seemingly stand on two legs. When Lincoln points out that he has never seen Charles do that, Luan says it is not Charles, and after tackling him, she pulls off the mask to reveal that the prankster is Lily. Luan is admittedly surprised by this revelation, but she demands her to stop with her prank. Lily refuses, and turns on the TV with her bone (which is revealed to be a remote), revealing the family driving in Vanzilla. At that moment, the family arrives to Burpin' Burger, and just before they can place their order, Rita gets a text from Luan saying that Lily is the prankster. As first, the family does not believe her, and while Lynn Sr. pinches on "Lily's" cheek, he inadvertently pulls off a mask to reveal Charles, much to the horror of the family. With the secret revealed, Lily activates her grand prank: she has the locks on Vanzilla lock the family in, and the car begins to drive around the Burpin' Burger building on an endless loop. Luan begs Lily to stop, but Lily lets out a fart cloud to escape.
Running upstairs, Lincoln and Luan discover that Lily fled to the attic. Upon entering the attic, they discover a console with numerous monitors showing the family screaming for their lives. At that moment, Lily arrives on her toy trike with a loaded diaper, ready to attack them. As Lincoln fights with Lily, Luan attempts to shut down the console and stop Vanzilla. After falling through the floorboards by a trap Lily set up, Luan uses a juice box to squirt juice onto the console, which successfully shuts it down and makes Vanzilla stop moving. Lily is initially disappointed her prank was foiled, but cheers up when Rita and Lynn Sr. vomit from all the motion.
Later that day, as the family sits in the living room, tuckered out from everything they went through, Lincoln, Luan and Lily approach them. Rita declares Lily to be grounded until age 16 (boosted to 21 after they get onion water dumped on them). However, Luan admits the onion water prank was hers, saying that because of Lily's actions, she feels reinvigorated and decides to come out of retirement. When Lily fist pumps with a "Yes!", Luan realizes that Lily deliberately pranked her family to get her out of retirement. Touched by this, Luan hugs her baby sister in gratitude, and Lynn Sr. realizes in horror that now, the family has somehow raised two pranksters.
Lori has no lines in this episode.