Twenty years ago, all the evil villains were banished from the kingdom of Auradon to the Isle of the Lost-a dark and dreary place protected by a force field that makes it impossible for them to leave. Stripped of their magical powers, the villains now live in total isolation, forgotten by the world.
Mal learns from her mother, Maleficent, that the key to true darkness, the Dragon's Eye, is located inside her scepter in the forbidden fortress on the far side of the island. The eye is cursed, and whoever retrieves it will be knocked into a deep sleep for a thousand...

Deep beneath the waves, King Triton's powerful trident has passed through the magical barrier that surrounds the Isle of the Lost-keeping villains in and magic out. And when Mal's longtime rival Uma, daughter of Ursula, gets wind of this, she can't believe her luck. The tide has dragged in something good for a change, and Uma is determined to get her wicked hands on it. But first, she needs a pirate crew.

A storm is brewing back in Auradon, and when Mal, Evie, Carlos, and Jay hear that the trident has been washed away, they realize they'll have to find it...