Having returned home, the boy and his grandmother then devise a plan to rid the world of witches. Learning the location of the Grand High Witch's Norwegian castle, they will travel there and use the potion to change her successor and assistants into mice, then release cats to destroy them before they escape. Using the Grand High Witch's money-making machine and information on all the other witches in various countries, they will then try to track down and eradicate them all over the world. The grandmother also reveals that as a mouse, the boy will probably only live about another nine years, but the boy does not mind as he does not want to live any longer than his grandmother.