Casey is writing a scary story for a local contest about ""Gooey Gus: the Slime Monster"", a doll that spits out grape bubblegum. Casey thinks her story isn't scary enough, so she asks for Lenni's help. Lenni adds atmosphere and writes how the Slime Monster is about to come after Casey. Alex and Gaby come to help, too, and Gaby writes about Alex and Jamal finding the Slime Monster seemingly alive in an alley, and then Alex, Gaby, and Casey find the Slime Monster in a crock pot.

Jamal, Lenni, and Alex are graduating from middle school and Tina is hosting the party, while Jamal and Tina work on the prom committee. However, the band that was supposed to play at the prom backed out. Jamal and Tina convince Lenni to play with Tina's brother Tuan. However, Lenni and Tuan get off to a bad start. Eventually, they learn to play their music together. In the meantime, Alex has been writing the story. He writes about the Slime Monster running away and kidnapping Gaby and about his attempts to save her.

Gooey Gus suddenly explodes in the sun and grows 6 feet tall in the story. Suddenly, at the band practice, Tina tells Lenni that he really likes her. If the gooey gum covers your skin, you are gone for good, so will Gaby and Casey make it?

The team trys to come up with a conclusion. Tina and Casey discover the Slime Monster's weakness, cold. Just before the discover their plan, He attacks Lenni and the rest of the team! Luckily, Tina escapes and Jamal and Tina melt the Slime Monster with vegtable oil.