When Eddie announces that he wants to become a full-time monster, his parents start to worry and encourage him to play with a normal boy. But when Eddie abandons the monsters to play computer games with his new friend, Fiend, Haggis and Norman create so much havoc that Nick finally snaps and dumps them in a forest.

Eddie pretends to be ill to avoid a maths test, promising the monsters they will have a great day hanging out together. But the monsters think they really have caught something - from Nick, who is at home, genuinely ill. So they make their own medicine which they test on Human Dad Thingy first.

The monsters become obsessed with all things shiny - especially money, the shiniest thing there is. So to get as much of it as possible, they set up a business in the basement - but what starts out as a bit of fun starts to go sour when the monsters turn into hard-nosed businessmen.