Act One

Milo lays in his room, alone. Some schoolmates of his come to his house and ask him to go to the park with him. He turns them down, and they complain that he never wants to do anything. Milo is never interested in anything at all. He hates, and is bored by, everything, especially school ("Another Boring Afternoon").

Three demons appear in Milo's room, although Milo does not know that they are there. They are pleased that Milo wants to do nothing and is bored with everything. They are doing their job in making sure of that ("Demon's Scene-Gotcha").

As the Demons disappear, the handles on Milo's dresser light up, and the front of the dresser opens to reveal the Phantom Tollbooth. There are two buttons: continue and cancel. Milo approaches and figures that there is nothing to lose. He presses continue. His room disappears as the tollbooth comes to life. Milo is given all of the instructions that he needs. He pushes a button and receives a coin... another button and he receives a map... and then his car arrives! He looks at the map and decides to go to the Castle in the Air. He deposits the coin, passes the tollbooth and is on his way ("The Birth of the Booth"). Milo drives down an unfamiliar country road, and neither his room nor the tollbooth are in sight. Everything seems brighter than Milo had ever seen before ("A Ride beyond Expectation").

Milo sees a man holding a sign on the side of the road and pulls up to him. The man welcomes Milo to the Land of Expectations. He explains that this is the place where everyone must stop before they get to where they are going. Many people never make it beyond this place, and this man's job is to rush them along. He is the Whether Man ("The Whether Man"). Milo asks if this is the right road to Dictionopolis. The Whether Man says that there are no wrong roads, there, so this must be the right one.

However, Milo begins to daydream and takes a wrong turn ("The Doldrums"). Milo stops and falls asleep behind the wheel of his car. The Lathargarians approach and inspect Milo. Milo awakens but realizes that the Lethargarians are harmless. He asks where he is, and they explain that he is in the Doldrums, which is where nothing ever happens or ever changes; thinking and laughing are illegal here ("Chaconne of the Lethargarians"). They explain to Milo what their days are like, here in the Dolodroms: nothing but eating, napping and procrastinating, which keeps them very busy ("The Lethargarian" / The Lethargarian Shuffle"). The only person in the Doldrums who ever does anything is the Watchdog. He approaches as the Lethargarians scatter. The Watchdog asks Milo what he is doing there. Milo says that he is on his way to Dictionopolis, and The Watchdog tells him that he got stuck here because he was not thinking... and the only way to get out is to start thinking. Milo begins to think about anything that he can, which gets him moving again ("The Drive to Dictionopolis"). Tock the Watchdog, tells Milo the story of Dictionopolis. Years ago, there were two princes born, one with a gift for words and one with a gift for numbers. The rift grew so great between them that each went his separate way and established his own land, Azaz became the ruler of Dictionopolis and the Mathemagician became the ruler of Digitopolis. Their sisters; the Princess Rhyme and the Princess Reason, tried to settle the quarrel. They ruled that numbers and words were of equal value. The brothers still could not agree, except that this answer from their sisters, equal importance, was wrong. They banished the two princesses to the Castle in the Air ("Tock's Narrative").

Tock and Milo arrive in Dictionopolis on market day. They find themselves in a market where words are being sold and bought. Milo is amazed by how many words there are and how many uses they have ("Welcome to Dictionopolis, At the Market"). While at the market, they meet the Spelling Bee, a large bee that never stings but can spell anything. They also meet the Humbug, an old beetle who is skeptical of everything. Milo tells him that since he seems so wise, he must be able to help them meet the King. The King's Advisors arrive and welcome Milo, leading him to the King. Since words are so important, they try to use all of them, even if they use four words in one sentence that all mean the same thing. Milo sees the downside to words, now, too: they can be very confusing ("The Spelling Bee"). The King agrees with Milo, that ever since Rhyme and Reason were banished, things seem to make little sense. Milo and Tock say that they want to try to rescue Rhyme and Reason and return them here. The King is cautious, saying that it would be a difficult job ("Entrance of King Azaz"). He warns Milo and Tock about all of the dangers that lay on the way to the Castle in the Air. He also tells them that his brother, the Mathemagician, would have to agree to their rescue, and if he knew that Azaz said yes, he never would ("Azaz's Warning"). Milo takes a moment to decide whether he is brave enough to take on this challenge and decides that he is ("Do I Dare"). The King gives Milo a dictionary to use on his way. The people of Dictionopolis gather to send Milo and Tock on their way ("Good Fortune to Milo and Tock").

Act Two

The road seems to have disappeared, so Milo and Tock are now on foot. They are carrying on, though, as the Demons watch. They wonder what Milo thinks he is doing. They cannot believe that he is trying to accomplish something and thinks himself to be important. They warn that they have ways of stopping him ("The Second Demon Scene"). The travelers seek out help. They meet a man who confuses them even more.He says he is a giant, a midget, a fat man and a thin man. They try to point out the problem with this, but he just sends them on their way ("Giant/Midget"). They meet Dr. Dischord and his assistants, the Deci-Belles. They specialize in noises, all sorts of noises, especially loud ones ("The Joys of Noise"). They point them to a sign that shows them the way to Digitopolis. It is actually three signs: one with miles, one with yards and feet, and one with inches. They cannot decide which one to follow. Dodecahedron, a mathematical figure with twelve different faces, greets them. They ask her which sign to follow, and she leads them on a shortcut. Milo is now very confused, because he is not good at problems ("The Dodecahedron").

They arrive at the Numbers Mine, where numbers originate, Milo is amazed to learn! Dodecahedron assures him that you must dig for numbers and it is very hard work. He wonders if it is worth it, since he feels that numbers are not even that important. The miners teach Milo the importance of numbers. After all, how can you have tea for two without numbers ("Hail Digitopolis – The Number Miners Number")? The Mathemagician arrives and greets his guests. He assures them of the importance of numbers over words. They sit down to lunch but feel hungrier than before. They had eaten the special of Digitopolis, Subtraction Stew ("The Mathemagician's Entrance, Subtraction Stew"). They discuss the confusion of things here since Rhyme and Reason were banished. Milo explains that he wishes to save them but he needs the Mathemagician's consent. As soon as the Mathemagician realizes that his brother, Azaz, has consented, he will not. He insists that they will never agree on anything, and unless Milo can prove differently, he may not go save Rhyme and Reason. Milo points out that they will always agree to disagree. Obviously proven wrong, the Mathemagician gives Milo a pencil to solve any problems that he encounters and sends him on his way.

Milo and Tock head into the Mountains of Ignorance as the demons anxiously await them. Milo and Tock go head to head with all of the demons who are trying to stop them. There is Trivium, the Demon of Worthless Tasks. He tries to enlist their help in filling his pool using eye droppers and untangling paper clips, all of which would take forever. There is The Demon of Insincerity, who keeps them running around in circles and gives them the worst advice. Finally, there is the Senses Taker who tries to bury them in questions and forms ("From Farewell Digitopolis through Mountains of Ignorance, The Senses Taker"). With the help of his pencil and dictionary, Milo manages to complete them all, and they begin the climb to the Castle in the Air. They reach the Princess Rhyme and the Princess Reason, who delight that someone is here to rescue them. They say how clever Milo must have been to get here, but Milo is filled with doubt, since he has no idea how to get them back safely past all the demons. They assure Milo that he has changed from who he once was and can now do anything ("Milo"). The Demons begin to destroy the stairway, and Milo, Tock and the princesses don't know how to get back down. Milo realizes that time flies and that Tock, who is a Watchdog, can get them down safely. As they land, the demons move in, trying to ambush them. They just about have them surrounded when the Kings and their armies, from both Digitopolis and Dictionopolis, arrive. The demons are outnumbered and retreat ("The Return of Rhyme and Reason"). It is declared that Rhyme and Reason reign over both kingdoms once more and that Milo and Tock are heroes. Milo heads for home and ends up back where he started. As he stands in his room, he looks around and see neither his car nor the tollbooth. There is a letter on his bed. It explains that now that he knows his way, he no longer needs the tollbooth, so it has been collected for other people to use. Milo is sure that he won't even have time to go on another journey, since he now realizes just how much he has to do right at home. His schoolmates come by again, and this time, Milo joins them, excited to go out and do things.