Milo goes in the tollbooth because he is bored and has nothing to do.
While in the Doldrums Milo meets Tock and they go to Dictionopolis and they meet Humbug and the Spelling bee. The king of Dictionopolis Azaz gives Milo letters to help him on the journey to get the Princesses safe of the Demons but he first has to get the permission from the brother of King Azaz the Mathmagician, because they both banished him
After Milo, Tock and the humbug get the permission from the Mathemagician, who gave them a magical staff for his journey he sets off for Princesses in the Castle in th Air
Milo, the humbug, and Tock are tricked by the demons while trying to rescue the princesses but they use the tools that the kings gave him and got away and rescued the princesses