Billy is a little boy who finds a monster sitting in his bed one night. When he runs to tell his nanny, she insists that there are no such things as monsters. She says Billy should believe her because she is bigger than he is and so she must be smarter too. She sends him back to his bed but when he returns, the whole room is full of friendly monsters who are all very different. Throughout the night, Billy and the monsters discover that just because someone is taller, orangest, furriest or stripiest doesn't mean they are smarter than anyone else.