Emily, an ordinary girl on land and a magical mermaid in the water, urgently needs relaxation, as her exhausted best friend Sona constantly reminds her after their adventures. Emily promises her that she will stop getting involved in dangerous situations and invites her, along with their friend Aaron, on a vacation with her family. But adventure is chasing her… Behind the waterfalls of the mysterious Forgotten Island, Emily discovers a hidden world that is not the paradise it initially seems. Thus, she finds herself entangled in an ancient prophecy, forced to discover the legendary giant that the islanders believe will save them. Will she manage to find the solution? Should promises always be kept? And what will happen if someone breaks them?

The seventh adventure of Emily, even more captivating and mysterious…