For 20 years, the truly treacherous and evil villains from the land of Auradon have been banished to the Isle of the Lost by King Beast. The dome covering their exile keeps them from accessing any magic. This leaves the formerly powerful antagonists to languish in pitiful obscurity with only their children to tell the tales of their glory days. Not only do they live without their magic, but those on the island survive on castoffs and leftovers.
Mal is the 16-year-old daughter of the island’s ruler, Maleficent. Her day starts off wrong when she wakes from a dream about a handsome prince from Auradon who claims to be her friend. Mal has no friends because her mother wants her daughter to be feared and hated like she was.
Mal does have one acquaintance, Jay, Jafar’s son. Jafar now runs a trinket shop. As they walk to school together, Jay tells Mal a new student is starting school — Princess Evie, the daughter of Snow White’s Evil Queen. Mal is more than surprised, as it was her mother that banished Evie and Evil Queen from Isle society because they had not invited Mal to Evie’s sixth birthday party. Mal decides to get revenge on Evie for the slight 10 years ago.
Evie is nervous about attending school for the first time, but excited, too. Life with her beauty-obsessed mother has gotten monotonous, and Evie longs to make friends. She does not help her cause when she accidently sits in Mal’s favorite seat. However, Evie does make a friend in Carlos De Vil, Cruella’s son. Although younger than the others in his class, Carlos is smarter than most of them. Mal has learned that Cruella is away for the evening and so insists that Carlos host a party that all her friends can attend. She also makes sure that Evie knows she is not invited.
Before the end of school, Mal changes her mind and decides that she can better exact her revenge if Evie comes to the party. Carlos enlists the help of his mother’s minions in order to get the house ready. The party begins around midnight, and in a surprising gesture of generosity, Mal provides toad’s blood shots for everyone.
When Evie arrives, Mal suggests they play a game called “Seven Minutes in Heaven,” in which a boy and girl are locked together in a closet. This time, however, Mal locks Evie in Cruella’s closet alone. Cruella has lined the floor with animal traps to prevent anyone from stealing her furs. Evie accidently sets off a chain reaction and barely escapes injury as the metal jaws snap shut throughout the closet. She manages to find refuge among the fur coats until Carlos gets her out.
Although Evie is supposed to be evil, she feels sorry for Carlos when she sees what passes as his bedroom. He has a mattress on the floor, with no blanket or pillow. His mother’s wigs take up the vanity. Even though it is against school and parental lessons, she offers to bring him an old comforter and pillow. Touched, Carlos shows her his science lab. He has been working on a machine that can punch a hole in the protective dome so they might be able to watch something else besides the television shows they always see.
When Carlos turns it on, it shoots a beam into the dome that, for a moment, pierces through it so they can see the night sky. Carlos’ television bursts to life and scans a wide variety of shows before dying out. Unbeknownst to either of them, in a distant fortress, Maleficent’s scepter and pet raven have been infused with magic and have returned to life.
In Auradon, Prince Ben, the son of King Beast and Queen Belle, is struggling. His father wants him to take on more responsibility within the kingdom so he can learn to be a king. Prince Ben is ordered to negotiate with the unhappy members of Sidekicks United. These underlings do most of the work in Auradon and feel they are not given enough to recompense for their labor.
Ben soon loses control of the meeting as the seven dwarves, Flounder, Genie and many other sidekicks nearly riot. He shouts the sidekicks down and adjourns the meeting without negotiating anything. The sidekicks leave, insulted by his rudeness.
Mal arrives home from the party to find her mother ecstatic by the return of her pet raven, Diablo. The bird has informed Maleficent that her staff, the Dragon’s Eye, has also come to life. She orders Mal to find it. Only then will Mal live up to her mother’s standards of evil and deserve her mother’s affection. Determined to succeed, Mal enlists Jay’s help. Jay is reluctant at first. But when his father learns the staff is on the island, he too, demands that Jay find it. But Jafar intends to sell it for a huge profit so he can again be rich.
Prince Ben redeems himself by reading the hundreds of pages of grievances filed by Sidekicks United. He then arranges a meeting with
Grumpy to discuss and negotiate on behalf of the two parties involved, King Beast and the Sidekicks. The negotiations go well with Prince Ben allowing new restitutions and payments for the Sidekicks’ work. Grumpy is impressed with Ben’s knowledge and bearing.
Evie overhears Mal and Jay arguing about their quest and tells them of Carlos’ invention, as it may explain how the Dragon’s Eye came to life. They visit his house, but when Carlos tries to make the machine work again, it does nothing but beep.
Evie suggest it is a signal reaching out to the Dragon’s Eye. As Carlos will not give up his invention, Mal forces him to come on the hunt with them. She also forces Evie to come because she secretly wants Evie to touch the scepter first. If she does, she will fall asleep for 1,000 years.
Maleficent said the Dragon’s Eye could be found in the Forbidden Fortress, but no one knows its location. The four teens bribe a teacher to get inside the Athenaeum of Secrets to retrieve a map of the island. With the location found, they set off together to find the scepter.
Once they find the fortress, each teen must solve a puzzle that forces each to confront the problems they have with their parents. Carlos answers questions posed by gargoyles on a bridge. He admits that his mother’s true love is not him, but her fur coats. The gargoyles allow the quartet to cross the bridge and enter the castle.
A room inside behaves like Jafar’s Cave of Wonders. It fills with sand, drowning the children until Jay states his father’s Golden Rule: “Whoever has the most gold, makes the rules.” Another room has a Magic Mirror that makes the teens look ugly. Before they can leave, Evie must recite the ingredients for a peddler’s disguise like the one her mother used to trick Snow White into eating the poisoned apple.
The teens bond closer together after each trial. Mal even finds herself letting go of her hatred of Evie so much so that when they finally do find the Dragon’s Eye, Mal stops her fellow travelers from touching it so that they won’t be cursed. Instead, she touches it and falls unconscious.
She has a vision in which she sees the day her mother, Maleficent, was not invited to Princess Aurora’s christening. She senses her mother’s anger and her pain at being overlooked. For the first time, Mal understands her mother’s motivation for being evil and seeking revenge. She is proud of how her mother raised her on her own, but sad because no one else understands how Maleficent is really just a hurt, little girl.
Mal wakes up to the others standing over her. She learns that the Dragon’s Eye disappeared when she touched it. Because Mal is part dragon, she could not fall under the 1,000-year spell. Mal and Evie bury any past animosity, and the four second-generation villains realize they are now, almost, friends.
Mal arrives home to find her mother holding the scepter, but disappointed with her daughter for not making one of the others touch it first. The stone inside, however, no longer glows, and Maleficent accuses Mal of breaking it. The other teens receive their parents’ chastisement as well when they return home. They join together to steal and wreak havoc on the marketplace. They are still evil descendants, but now they have each other.
Prince Ben thinks about how his life and those of the children on the Isle of the Lost are similar. They have not been given a choice in their destiny. He must become king because his father is king. They are forced to live on the Isle of the Lost because their parents are evil. In a moment of inspiration, he comes up with a way to change life in Auradon and on the Isle. He runs off to discuss his idea with his parents.