Alert! Zombie Invasion! is a Halloween special and episode from Season 1 on the show called Three Lionhearted Kats.
When everyone at the Flosyce Academy dance party had a new taste of Ashley and Nadia's Strawberry Paradise smoothies (despite of the Katroids' Lemony Juice), Madame Twilight creates a virus mixed with the smoothies infecting the students and turning them into licking zombies.
There was a school dance party in the nighttime at Flosyce Academy where the students were having fun playing games, eating food, and dancing. Sprucia, Gilli, and Isaak were making a lemonade stand in order to beat Ashley and Nadia opposing their smoothie special. Prince Charles, Arthur, Bridget, and the rest of the students tried their lemonade first. They became disgusted and appalled, they tried Ashley and Nadia's next. Gilli and Isaak tests their lemonade, they were disgusted too and went to try the smoothies. Without the assistance of her siblings, Sprucia walks to the garden to grab some more lemons and fruit attempting to beat the Olyvord sisters.
Meanwhile, Madame Twilight invisibly appears at the party. She sees students drinking the strawberry smoothies, she then applies a sparkling virus in the smoothies (except Gilli and Isaak's). When they tasted the embedded virus mixed with the smoothies, they start to feel dazed, sick, and ill. Everyone turns into yellow-spotted long-tongued turquoise zombies, mind-controlled by Twilight. After when Ashley and Nadia were infected by them, they cornered Gilli and Isaak and they become licked too.
Sprucia was on her way back to the party until she walks in and suddenly all zombies spotted her, she avoids them of their treacherous infectious tongue climbing on the roof but encountered infected Gilli and Isaak and screamed frighteningly, Sprucia pushes them out of the way. She infiltrates the school using a window to a hidden room and sets a barricade in the entrance to give the zombies more time to knock it down. Sprucia uses her vision power to find what caused the outbreak, she senses Twilight who caused the infection by applying sprinkles into the strawberry smoothies but not in the lemonade stand. Then she has an idea, Sprucia can go to the science lab to make a potion to turn the students back to normal.
After making a cure, she applies it on Gilli and Isaak as a test. They're both turned back to normal, but is licked and turned back into zombies. Sprucia needs to make more cure, so she heads back to the lab. Reuben was in the lab and Sprucia asks him to help cure the infected, she can use the disgusted lemonade juice that she and her siblings made to mix it with the cure. The zombies tear down the barricade, Sprucia and Reuben quickly set the attack. Reuben sets up the pump then Sprucia aims for the zombie's tongue, splashing them entirely. All students were turned back to normal and disgusted of the salty lemonade. Twilight attempts to escape but is caught, she is arrested by the knights. Everyone and Reuben resumes having a dance party again.