Avsnitt 4

Big thinks that Small is creating a mess all over the house and invents a machine which tidies away all of Small's debris. Small, shocked, tells Big that the pile of dirty socks Big has just sucked into his machine is actually a scientific experiment and that the old red jelly lid is a model of the planet Mars! Small decides to walk away and find some place else to live in - and discovers, through a mouse hole, a neat little room where he builds a fort from a sofa and bounces on the bed... 'What is going on in here!' cries Ruby, the pink mouse, whose home it is. She is not impressed with the fort. Big intervenes to calm her down and decides that the best thing to do is build Small a space of his own where he can be - well, where he can be Small! Big and Small introduce themselves properly to Ruby. Small drives through a hole in the wall and discovers a mysterious room.