In the land of monsters, there becomes an energy shortage. They get their energy by entering childrens closets and using their screams as a power source. Mike and Sully have to work overtime, and when they do, they notice someone leaves a door open, and a child is set free in Monster Land. Children being evil and harmful creatures to monsters, there is a hunt for the young girl, and Mike and Sully have to try their best to keep her safe, and get her back home.