In a city named Amity Park, a young teen named Danny Fenton and his best friend, Tucker Foley, are gawking at a large truck/SUV. They are gawking over its chrome wheels, huge engine, interior space, and other things that guys like. Sam Manson, they're female best friend, is more concerned about things such as the environment. "Seats made of owl leather, interior wood paneling from the Amazon rainforest, 12 gallons to the mile? This thing is an environmental nightmare!" she cried after looking at the sticker on the window.
She wanted Danny to destroy the vehicle, but nothing she tried worked. She walked off in disgust. Under her breath she wished someone would destroy the trucks. Desiree, a wish granting ghost, hears her and grants the wish. A giant cow from a nearby restaurant comes to life and begins destroying the truck. Danny and Tucker try to protect one and are covered in milk. However, Danny goes ghost and is able to defeat the cow.
On their way to school, they pass a billboard for the movie Trinity of Doom, which comes out on Friday. The movie is a battle between Sam's three favorite female movie monsters. She excitedly informs the boys that she's already bought tickets for Friday night. Suddenly, a popular girl named Paulina walks up and invites them to her party, saying that she's inviting Tucker and Sam so that Danny will come, and she's inviting him in hopes that the ghost boy will show up.
The boys manage to convince Sam to let them go, instead of going to the movie. As they walk off, Sam unintentionally wishes something would happen to Paulina so the party would be cancelled. Desiree hears her and grants the wish. During the day, the three monsters from the movie separately attack Paulina. Danny saves her all three times, but all three monsters say Sam's name. Danny begins to think Sam may be the cause of all this, or at least a part of it. He gets her to wear the specter deflector just in case, protecting her from ghosts.
After school, Danny and Sam end up walking home together. Sparked by a single comment, Danny and Sam end up bickering in a fight, and Sam declares "Danny I swear, some days I wish I'd never even met you!" Eavesdropping, Desiree decides to grant her "wish". However, the specter deflector prevents Sam from being affected.
The next morning, Sam goes to school and tries to apologize to Danny. "I'm sorry, do I know you?" he responds. Sam quickly realizes what's wrong, and attempts to tell Danny who she is. He is not convinced. After hearing that a popular girl named Paulina is having a massive birthday party that night where everyone will make a wish during the expected meteor shower, Sam knows what Desiree is planning. Since she grows more powerful with each wish, all those wishes will make her unstoppable.
Sam tries twice that day to get Danny to come with her to his parents' lab and become a ghost again, but to no avail. Knowing time is running short, she makes the decision of her life. She sneaks into the Fenton's backyard when Jack, Danny's father, goes to check the mailbox on the street behind the house. From the yard she sneaks into the house, and down to the deserted lab. She grabs the white and black jump suit that Danny had worn when he went into the portal to the ghost zone, pulls it on, rips Jack's face off the front (XD), places a custom S in its place, and enters the portal. She presses the on button, and it whirrs to life. The portal zaps her as it comes to life, and she is knocked unconscious.