Mad Scientist Tasha sends her assistant, Austin, to give invitations to the Mummy King, the Werewolf, and the Vampire for her "best creation ever", which is actually a birthday party for Austin!
Austin exits the fence dividing his house from the others' houses. He introduces himself to the viewer as Austin, and explains that today is his birthday. He then shows the viewer Tasha, who is playing with toy beakers and wearing a wig and glasses. Austin tells the viewer that she is Mad Scientist Tasha, and he is her assistant. Austin asks Tasha if she knows what today is, hoping that she would answer with "your birthday", but Tasha tells him that today is the day that she finishes her greatest experiment ever as she sings I Got a Secret. She tells him to go to her laboratory.
She sings a reprise of I Got a Secret after the backyard turns into a dark lab filled with tables covered with beakers and inventions. The mad scientist tells Austin to go get a beaker from a table at the right. Austin walks off sadly. Tasha tells the viewer that she does remember Austin's birthday and is throwing him a surprise party. Austin walks closer in range. Tasha tells Austin that today he is given a very important mission: to retrieve three monsters, the Mummy King, the Werewolf, and the Vampire, and hand them an invitation. She tells him to get going and bring all of the monsters back to the laboratory after gathering them together.
After Austin walks away out of the laboratory, Tasha tells the viewer that the monsters are the party guests for the birthday party she is throwing for Austin. Meanwhile, Austin tells himself that today is the worst birthday ever as he walks inside the mummy's pyramid. He does not see anyone inside, so he walks in. He reads some hieroglyphics on the wall and reads that he should not go forward.
He walks forward, even though the hieroglyphics told him not to, and reads more. He reads that he "asked for it", and he should not step on any X's. He then realizes that the tiles on the floor he is standing on are all X's. Boulders fall from the ceiling and try to crush Austin. Austin is quick and escapes all the boulders, entering a chamber in which a large tomb is located. A moaning sound comes from inside the tomb, and it is Mummy Tyrone.
Tyrone explains that he thinks Austin is a monster and exits the tomb. He sings Scared Of You until he realizes that Austin is not scary. Austin gives Tyrone a note that invites him over to Austin's surprise birthday party. Austin asks what does it say, but Tyrone says that it is a secret. They walk to the werewolf's forest and Tyrone asks if this is the laboratory. Austin answers no and says that it is the werewolf's forest. Tyrone is scared of the werewolf and he and Werewolf Uniqua put their description of how they are scared of each other in the second verse Scared Of You.
They realize that they each are not scary, Austin gives Uniqua a note that invites him over to Austin's surprise birthday party. Austin asks what does it say, but Uniqua says that it is a secret. They walk on to the vampire's castle, Uniqua asks if it is the laboratory, and Austin tells her that it is the vampire's castle. They enter and read a sign that says that they cannot go forward. They do go forward and read another that says that they asked for "it". Uniqua is confused at what they asked for until the stairs fall into a pit. They run and scream up the stairs.
They enter a door and see the vampire on the ceiling. Tyrone and Uniqua and Vampire Pablo descuss how Pablo is afraid of Mummies and Werewolves like Tyrone and Uniqua, and how vampires like Pablo scare the living daylights (or should I say nightlights) out of Uniqua and Tyrone in the form of Scared Of You's final verse. They realize that they are all not scary and Austin gives Pablo the letter. Austin asks what does it say, Pablo first says "Well..." and Austin says "Yeah, I know. Is a secret.". They dance to the laboratory while singing Hurry Home. They all enter the laboratory and look around. Tasha silently shows the monsters a secret way inside the party room.
Austin finds that the monsters are all gone and thinks that he lost them. Austin enters the darkened laboratory through the main doors. The lights turn on and the party starts. They sing Monster Dance Party as they show off their dance moves. Uniqua invites the four all over to her house for pumpkin pie. They accept as the laboratory transforms back into the backyard. They sing the end song and enter Uniqua's house. Austin opens the previously closed door and shouts "Oh, brother!".