The first act of Wicked starts with the Ozians’ celebration of Elphaba’s death, the Wicked Witch of the West. When Glinda arrives, the Ozians inquire about Glinda’s connection with Elphalba. Glinda confirms that she one knew Elphalba.
As the scene changes, Elphalba comes in with her green skin. A product of an affair between her mother and mysterious man possessing a green elixir, Elphalba is greatly despised by his supposedly father, the governor of Muckinland. Elphalba and her disabled sister, Nessarose, go to Shiz University. Glinda also goes there where she turns out to be one of the more popular students. Nessarose is given by their father a pair of silver slippers and is taken by Madame Morrible, the headmistress, under her care. Elphalba’s frustration about her sister being taken away from her awakens the power inside her. The explosion she causes catches the eye of Madame Morrible and she decides to put Elphalba under her tutelage.
Her education about sorcery makes Elphalba Galinda’s greatest rival. Rumors also start spreading regarding the animals who can speak.
A young prince named Fiyero arrives at Shiz. Galinda is smittened by him and badly wants to be with him in a school party. So she can go out the prince, Galinda convinces a Munchkin named Boq to ask Nessarose to the party instead of her. She also offers Elphalba a hat that she can wear in the celebration.
In the party, Madama Morrible tells Galinda that she also wants her to be her students. Meanwhile, other students laugh at Elphalba when they see her wearing a witch’s hat. This makes Galinda feel bad and she decides accompanying Elphalba for the rest of the night.
When they get back to their room, the two girls share their stories to each other. Galinda confesses her feelings for Fiyero while Ephalba thinks that her father blames her for her mother’s death. At that moment, Galinda resolves to help Elphalba gain more attention in their school. However, Fiyero tells Elphalba that she’s good just as she is. Their only animal professor, Dr. Dillamond, arrives and announces that he can’t teach anymore. The school also releases a cage that will prevent animals from talking. This enrages Elphalba. When no wants to side with her, her anger explodes and she escapes with lion cub in the cage and Fiyero.
Afterwards, Madam Morrible informs Elphalba that the Wizard wishes to see her. When her friends come to see her off, Elphalba asks Galinda, who now calls herself Glinda, to accompany her to Emerald City.
When the two girls meet the Wizard, he gives Elphalba a book of sorcery. Elphalba tries a spell that is supposed to make the Wizard’s servant monkey to float but it grows wings instead. Elphalba concludes that the Wizard must be the one who is behind the movement that tries to prevent the animals from talking. It also turns out that he can’t do any magic at all and he just used Elphalba to use the Grimmerie book of sorcery. The Wizard try to convince Elphalba and Glinda to join him but Elphalba refuses and runs away. On the other hand, Madam Morrible sends out rumors about what Elphalba did with the monkeys and makes her “wicked” in the eyes of the people. Because of this, Elphalba decides to live alone and stay away from people who will just let her down.
In the second act, Elphalba is now known as “Wicked Witch of the West” while Glinda has become “Glinda the Good.” Fiyero, now the Captain of the Guard, is not too happy when Madam Morrible engages him to Glinda.
Meanwhile, Elphalba visits Nessarose who is now the governor of Munchkinland. Nessarose does not believe anything that her sister says. To make her believe her, Elphalba casts a spell and treats Nessarose’s legs. Nessarose shows that she can now walk to Boq but it does not please him. Because of this, Nessarose grabs Elphalba’s spell book and casts a spell that will make Boq fall in love with her. However, it only damages his heart. Elphalba tries save him by turning him into a tin man. When Boq wakes up, Nessarose tells him that Elphalba was the one who put a spell on him.
When Elphalba goes back to the Wizard’s palace, the Wizard once again encourages her to join him in his crusade but Elphalba firmly refuses as she remembers that he’s the one that caused the animals to lose their skills in speech. At that moment, Glinda comes with Fiyero but Fiyero helps Elphalba to escape. Glinda concocts a plan to lure Elphalba out by using her sister.
During their escape, a vision comes to Ephalba showing that her sister is in grave pain. Elphalba goes right away to help her.
Elphalba arrives and sees that Nessarose has been crushed by house where a girl named Dorothy can be found inside. She sees Glinda and argues with her. When the guards arrive to arrest her, Fiyero comes to save Elphalba again. Glinda warns the guards not to hurt Fiyero but in the end, Fiyero gets injured. When Elphalba can’t save him, she becomes enraged and decides that from that moment on, she will truly live as the wicked witch.
The citizens of arrive with urging of Madam Morrible and Boq. Glinda realizes that Madam Morrible caused the death of Nessarose. She then goes right away to warn Elphalba that the townspeople are on their way to kill her.
When Elphalba catches Dorothy, demanding Nessarose’s slippers. Glinda arrives and she tries to convince Elphalba release Dorothy. A letter arrives confirming Fiyero’s death which cause the two women to reconcile. Ephalba hands over the Grimmerie to Glinda and tells her to hide. While Glinda is hiding, Dorothy throws a bucket of water to Elphalba. Glinda is surprised to see Elphalba melts. When she checks out what happened to her, only her hat and the small bottle of green elixir that she has always kept are the things left remaining.
Glinda heads back to the Wizard’s. When the Wizard sees the green bottle, he realizes that Elphalba was her daughter. As the Wizard suffers in his grief for her daughter, Glinda commands him to leave Oz and she imprisons Madam Morrible for evil deeds.
Meanwhile, the Scarecrow who turns out to be Fiyero, arrives at the place where Ephalba supposedly has died. From a trap door on the floor, out comes Elphalba. It turns out that she turned Fiyero into a scarecrow and faked her death so that they can be together at the end.