9 years ago . . .

Being the other daughter of the Little Mermaid, Diana always had a love for adventure and obtains the ability of transforming into a mermaid just like the rest of her family. But when she accidentally swims towards the Isle of the Lost, she begins an unlikely friendship with Harry, son of Captain Hook, with only the invisible barrier separating them. Will their friendship turn into something more? Or will their bond cause something worse between Auradon and the Isle of the Lost?