When the magical waters of the Pirate Stream begin flooding Marrill's world, she must return to the Stream and find the source of the mysterious Iron Tide.

Reunited with her best friend Fin - who has been forgotten all over again - Marrill must make the treacherous trek to the impossible world of Monerva and uncover the secrets of its long-lost wish machine. Only there can Fin wish to finally be remembered. Only there can Marrill wish to save her world and the people she loves.

But to get everything they've ever wanted, Marrill and Fin may have to give up on the most important thing they already have: each other.