Arthur answers a distress call from Princess Selenia, who is menaced by the nefarious Maltazard.

With Maltazard now seven feet tall and Arthur still two inches small, our hero must find a way to grow back to his normal size and stop the Evil M once and for all, with the help of Selenia and Betameche.

Arthur is a spirited ten-year old whose parents are away looking for work, whose eccentric grandfather has been missing for several years, and who lives with his grandmother in a country house that, in two days, will be repossessed, torn down, and turned into a block of flats unless Arthur's grandfather returns to sign some papers and pay off the family debt. Arthur discovers that the key to success lies in his own descent into the land of the Minimoys, creatures no larger than a tooth, whom his grandfather helped relocate to their garden. Somewhere among them is hidden a pile of rubies, too. Can Arthur be of stout heart and save the day? Romance beckons as well, and a villain lurks.