Mal, Evie, Carlos, and Jay have received threatening messages demanding they return home. They have a sneaking suspicion that their villainous parents are behind the messages, and something Evie sees in her Magic Mirror confirms their fears. Although Maleficent's just a tiny lizard after her confrontation with Mal, could she have found a way to escape? Mal and her friends determine to sneak back to the Isle to get to the bottom of the mystery.

Twenty years ago, all the evil villains were banished from the kingdom of Auradon and made to live in virtual imprisonment on the Isle of the Lost. The island is surrounded by a magical force field that keeps the villains and their descendants safely locked up and away from the mainland. Life on the island is dark and dreary. It is a dirty, decrepit place that's been left to rot and forgotten by the world. But hidden in the mysterious Forbidden Fortress...