Dorothy is seen with her Aunt Em, Uncle Henry, and dog, Toto, on their farm in Kansas. She expresses her desire to get away from the farm life and see distant lands. Aunt Em and Uncle Henry urge her to stay, telling her that she has everything that she could ever want here at home ("The Feeling We Once Had").
A tornado hits and lifts the farmhouse, with Dorothy and Toto inside, right up into the air. ("Tornado"). It comes to rest with a bump, in the middle of an emerald green field covered with flowers. There she is met by the Munchkins who are all dressed in blue and Addaperle, the Good Witch of the North, who tells her that her house has fallen on the Wicked Witch of the East, and killed her, freeing the Munchkins from her evil powers. Dorothy, distressed and confused, wants only to return to Aunt Em, Uncle Henry, and Toto in Kansas, and Addaperle decides her best bet is to go and see the great and powerful Wizard of Oz ("He's the Wizard"). She gives her the Witch of the East's silver shoes, and tells her not to take them off before she reaches home, for they hold a very powerful charm.
Dorothy sets off down the yellow brick road, full of doubt and fear at what lies ahead ("Soon As I Get Home"). Stopping to rest by a cornfield, she is startled when a Scarecrow hanging on a pole strikes up a conversation with her ("I Was Born the Day Before Yesterday"). He tells her of his longing for brains so that he can be like other people, and she invites him to accompany her to see if Oz can help him ("Ease On Down the Road #1").
The yellow brick road leads them into a great forest where they discover a man made of tin, rusted solid. They oil his joints ("Slide Some Oil To Me") and he tells them how, to prevent him from marrying a servant girl, the Wicked Witch of the East put a spell on his axe so that it began to cut off parts of his body. Each time it happened, a tinsmith replaced the missing part with one made of tin until he was entirely made of it. The one thing the tinsmith forgot was a heart, and the Tin Man has longed for one ever since. Dorothy and the Scarecrow invite him on their journey to see the Wizard with the hope that he may give him one ("Ease On Down the Road #2").
The yellow brick road leads them into a dark jungle where they are attacked by a large lion ("I'm a Mean Ole Lion"), but are unharmed because he is a coward. When he learns where they are going, he asks if he may accompany them to ask the Wizard for some courage. They agree and the trio becomes a quartet ("Ease On Down the Road #3"), but face a new danger when they are attacked by half-tiger, half-bear creatures called Kalidahs ("Kalidah Battle"). After a great fight and harrowing escape, they stop by the road to rest. The Lion is embarrassed by his cowardice in the battle, but is comforted by Dorothy's kind words ("Be a Lion").
Seeing a green glow in the distance, they continue their journey to the Emerald City, and wander into a field of poppies who blow opium dust on them. Not being made of flesh, the Scarecrow and Tin Man are unaffected, but Dorothy and the Lion begin to become disoriented and drowsy. Dorothy recalls that the Munchkins warned her of the dangerous poppies, and runs from the field as fast as she can with the Scarecrow and Tin Man behind her. The Lion is overcome by the dust and begins to hallucinate ("Lion's Dream"). He is dragged from the field and returned to his friends by the Field Mice who police the area.
Marching up to the gates of the beautiful Emerald City, they are met by the Gatekeeper who insists they must all be fitted with a pair of green tinted glasses that are locked on to prevent their eyes from being blinded by the dazzling sights. They enter the city and look about in awe at the richly dressed people that inhabit this magnificent place ("Emerald City Ballet"). The haughty and condescending people laugh and ridicule this odd party for wanting to see the Wizard until they see that Dorothy is wearing the Witch of the East's silver shoes. The quartet is shown right into his palace.
Once in the throne room, they are assaulted by a great show of lights, smoke, and pyrotechnics as the Wizard appears in several forms before them ("So You Wanted To See the Wizard"). They each plead their case to him, and the Tin Man imagines how life would be with a heart ("What Would I Do If I Could Feel"). He agrees on one condition: they must kill Evillene, the Wicked Witch of the West. Dorothy and her companions sink to the floor in tears as their goals seem farther off than ever.
Evillene rules over the yellow land of the west, enslaving its people, the Winkies. She is evil, power hungry to get what she wants ("Winkie Chant/Don't Nobody Bring Me No Bad News"). Seeing Dorothy and her odd friends approach, she sends her Winged Monkeys to kill them ("Funky Monkeys"). They dash the Tin Man against rocks until he can no longer move and rip the stuffing out of the Scarecrow also leaving him helpless. Seeing Dorothy's silver shoes, they dare not harm her. They carry her and the Lion to Evillene's castle instead. While searching for a way to get the powerful shoes from Dorothy, she forces her and the Lion to work doing menial chores. She takes delight in torturing the Lion before Dorothy which angers her. She picks up a bucket of water and throws it at her. She melts until there is just a wet, gold cap on the floor. Her spell on the Winkies is lifted, and they show their thanks by restoring the Tin Man and Scarecrow to top condition, and reuniting the four friends ("Everybody Rejoice").
Returning to the Emerald City, they see the Wizard (now a booming voice that seems to come from the very air). He reneges on his promise, and the Lion knocks over a screen in anger. Behind it stands a bewildered man who claims to be the real Wizard ("Who Do You Think You Are?"). He shows them the elaborate mechanical effects used to create his illusions, and tells them that he is really a balloonist from Omaha who traveled to Oz by accident when his hot air balloon drifted off course. The people of Oz had never seen such a sight and proclaimed him Wizard. Not wanted to disappoint them, he assumed the role and had a great city built. He then had everyone in it wear green glasses, and in time, the people came to believe it was green.
The angry quartet confronts the Wizard on his deceptions, but he points out that the Scarecrow, Tin Man, and Lion already have the things they seek as shown in their behavior on the journeys they have made ("Believe In Yourself"). They remain unconvinced so he creates physical symbols of their desires and they are satisfied. He proposes that Dorothy can return to Kansas the way he came, and offers to pilot her in his hot air balloon. He addresses the citizens of the Emerald City in person for the first time in many years, telling him of his imminent journey, and leaving the clever Scarecrow in charge ("Y'all Got It!"). Just as his speech reaches its climax, the balloon comes free from its moorings and rises quickly into the air, taking Dorothy's hopes of getting home with it.
There is a flash of light and Addaperle appears, suggesting that Dorothy ask Glinda, the Good Witch of the South, for help. She transports them to Glinda's palace in the red land of the south ("A Rested Body Is a Rested Mind"). Glinda is a beautiful and gracious sorceress, surrounded by a court of pretty girls. She tells Dorothy that the silver shoes have always had the power to take her home, but like her friends, she needed to believe that fact before it was possible ("If You Believe"). She bids a tearful goodbye to her companions, and as their faces fade into the darkness, she thinks about what she has learned, gained, and lost ("Home"). She taps the heels of the silver shoes together three times, and as Toto jumps into her arms, licking her face, she knows that she is back home at last ("Finale").