So when he gets the tollbooth as a present, he decides to go through it, ending up in the lands beyond.
First, he explores the Doldrums. Everyone who lives there is bored and does nothing. Luckily, Milo meets the watchdog Tock, who helps him escape.
Milo and Tock go to Dictionopolis, where they meet the Spelling Bee and Humbug.
After a food fight, Milo ends up in jail, where he meets Faintly Macabre. She tells him that two princesses named Rhyme and Reason have been exiled from Wisdom.
Milo and Tock leave the jail and head over to the king's banquet, where people eat words. Naturally.
After the banquet, the king gives permission for Milo to rescue the princesses. And so, with Tock and the Humbug, Milo heads to Dictionopolis.
Milo and his friends have a few adventures on the way: Milo meets Alec Bing and learns about viewpoints; he meets an conductor whose orchestra plays colors; he meets Dr. Dischord and the DYNNE; and finally he ends up in the Valley of Sound, which is silent.
Milo goes into the valley's fortress and helps the sounds break free.
Before moving on, the group accidentally takes a sideways trip to the Island of Conclusions.
Then Milo and his friends meet the Dodecahedron and Mathemagician, at which point Milo learns about numbers and takes a side trip toward Infinity (he never does make it there).
Milo fools the Mathemagician into agreeing with King Azaz, and gets permission to rescue the princesses.
Milo and his friends climb toward the Mountains of Ignorance. They defeat three demons and a giant before making it to the Castle in the Air. To defeat each demon, Milo uses one of the gifts he had received earlier on his journey.
The Senses Taker tries to fool Milo and the others from getting into the Castle, but Milo accidentally breaks his spell with the fourth gift.
Milo and the others go into the castle and meet the princesses. And in the end, they all escape, thanks to some help from Wisdom's armies. Success!
Everyone celebrates for three days, but then Milo heads home, back through the tollbooth.
The next day, the tollbooth's gone, and Milo is ready to starting having some adventures on his own.