Tock, carrying Milo, the Humbug and the princesses on his back, glides down from the Castle in the Air and lands with a sudden jolt. The group quickly begins running down the Mountains of Ignorance as the horde of demons spots them and follows. Milo casts a glance over his shoulder and sees a horrible host of monsters that appears to be gaining on them. Just as the demons have caught up and are poised to pounce, they inexplicably stop in their tracks. Milo looks up and sees the armies of Wisdom, led by King Azaz and the Mathemagician, galloping towards them. The demons turn tail and run back up into the dark places from which they came.
A huge celebration ensues and all of the people Milo met during his journey through the Lands Beyond show up to congratulate him for finding Rhyme and Reason. King Azaz finally tells Milo the "secret" he warned him about back in Dictionopolis: the mission to save Rhyme and Reason was actually impossible. The king explains that he kept this from Milo because "so many things are possible just as long as you don't know they're impossible."
After Milo and his friends enjoy an joyous celebration, the princesses tell Milo that it is time for him to return to his home. He exchanges goodbyes with all the people he has met in the Lands Beyond, including his friends Tock and the Humbug, and sets out on the highway in his electric car.
Milo comes upon a tollbooth like the one he assembled in his bedroom and passes through it to find himself right back where he began. He realizes that days or weeks have passed while he has been away and hopes that no one has been worried. As it turns out, however, only a few hours have passed. It is near nightfall and Milo, who is exhausted, decides to go to bed.
The next day begins like any other. Milo goes to school where he is distracted by thinking of making his next trip through the tollbooth. He rushes home from school planning to hop in his electric car and have another adventure. When he reaches his bedroom, however, he finds that the tollbooth is gone. In its place is a note addressed "FOR MILO, WHO KNOWS THE WAY." The note explains that there are many more boys and girls in need of the tollbooth and suggests that, thanks to the lessons he has learned, Milo can explore many more wonderful lands all by himself. The tollbooth was just the first step, it seems, and now Milo is free to do all the exploring and adventuring he desires. Milo contemplates this, looking around at his room in a whole new way and seeing all sorts of wonderful and interesting things. "Well I would like to make another trip," Milo thinks, "but I really don't know when I'll have the time. There's just so much to do right here."
In this final section, Juster brings his major themes full circle. Throughout The Phantom Tollbooth, Milo has been learning how to appreciate and find the beauty in the things all around him as well as the value of education. When Rhyme and Reason return to the Kingdom of Wisdom and Milo himself returns to his home, these lessons are completed, and we see Milo in a whole new light.