In Monsters, Inc., a child, considered the most toxic thing alive, is loose in Monstropolis, and it's all Sully's fault. Or is it? This is the family movie about Sully and Mike's big adventure, and how they solve both the energy shortage in Monstropolis and the question of why the child's door was left open after quitting time.
The Child Arrives
Mike and Sully work at Monsters, Inc., the company that provides all the energy needed to run Monstropolis. There's a serious energy shoratge, and good scarers are in short supply. Scarers work to generate energy by entering children's rooms during the night and making them scream. The more and the louder the screams, the more energy generated. There's an incentive program, of course, and the competition is fierce. But the top two contenders are Sully and the slithery, slippery Randall.
One night, Sully returns to the scare floor to take care of some paperwork while Mike is out on a date, and he discovers a door that has been left out. He opens it to see who's working late, but there's no one there. When he closes the door, he is horrified to discover that the child has left her room and entered Monstropolis. He tries to put the child back in her room, but she moves too quickly for him. Then he hears someone coming onto the scare floor, so he scoops up the child and runs.
Not sure how to handle this dreadful situation, Sully goes to the restaurant where Mike and Celia are celebrating her birthday. He takes the child along in a Monsters, Inc. duffel bag. But she escapes into the restaurant and causes mayhem. Sully and Mike scoop up the child and run for it ... but they leave the duffel behind in their panic. Celia, too, gets left behind and is rounded up for decontamination.
Trying to Return Boo Home
All of Monstropolis is in an uproar. Mike and Sully decide that the only thing to do is smuggle the child, whom Sully has named "Boo," back to the scare floor at Monsters, Inc., call up her door, and shove her in before anyone comes to work. There's a hitch. Not only does Randall think Mike and Sully have something to do with the escaped child, but Roz, the company's records librarian, thinks Mike is a bit of a shady character. So they are under surveillance. And then the child escapes from them again.
After a frantic search, Sully finds her, and then Mike tells Sully that he will have her door ready at lunchtime, when the scare floor will be empty. But when they arrive at the scare floor, Mike lets slip that it's Randall who prepared the door. Sully doesn't trust Randall and refuses to put Boo into her room. Mike goes in to prove it's safe, and he's captured by something hiding out of sight in the room. Sully and Boo hide, and Mike is taken away ... by Randall. Sully and Boo follow, and they discover a secret workshop deep in the factory, where it transpires that Randall is working on a machine that will simply suck the screams from children, eliminating the need for scarers.
Sully rescues Mike, and they go to the company head, Mr. Waternoose, to reveal the plot. Mr. Waternoose takes the child and calls up a door. Only it isn't Boo's door. He shoves Sully and Mike through, banishing them to the human world. Mike is furious with Sully, and it looks like the friendship may be over. But Sully, realising that, somehow, Mr. Waternoose is involved with Randall's horrible project, is determined to return to Monstropolis and save Boo. He manages to get to a village and get through an open door, and he reaches Boo just in time. But he still has to outwit Randall and defeat the plans that he and Waternoose have laid.
The Great Chase
Sully and Mike go looking for Boo's door, but Randall and Waternoose are too close for them to risk trying to return her. So Sully decides to take a ride on the door until they get to the door storage area. Thus begins the great chase, through door after door, with Randall right on their heels. Finally, they capture Randall and banish him to the human world. They then return to Boo's door to send her home. But Waternoose has called up her door and is preparing to turn Mike and Sully over to the CDA -- the group that handles child contamination problems. It's only when Sully remembers the door portal in the training room that Mike and Sully are able to plan a way to catch Waternoose and return Boo home safely. But will they ever see her again?
Solving the Energy Crisis
Mike and Sully have saved the child, but the company is toast. The scandal with the child's escape has destroyed its reputation, and, without screams, Monstropolis will not survive long. But a chance remark of Mike's reminds Sully of a very important thing that Boo showed them ... and they are able to save the company and reverse the energy shortage, restoring the company's reputation and skyrocketing Monsters, Inc., into record-setting profits.
Sneaky Tricks in Monsters, Inc.
Monsters, Inc. is a Disney film animated by Pixar. That being the case, the film has many references to prior Pixar films and shorts. The toys in Boo's room, and various incidents within the movie, will bring back favorite Pixar memories for in-the-know viewers.