You know when your were little, and you thought monsters came through your closet and scared you? Well, don't take it personally. It was just a job. Monsters depend on the screams of human children to power their city, Monstrapolis. So they climb through the closet doors of kids around the world, and store the screams at Monsters, Inc. This is dangerous work, as every little monster knows that nothing is more toxic than a human child - "a single touch could kill you!" So when the city's top scarer Sully and his friend Mike accidently let in a human child named 'Boo', they'll do anything to get her back into the world she came from.