Once there was a man who fell in love with a mermaid. He swam down into the sea to be with her, and was never seen again … When Sapphire’s father is lost at sea, she can’t help thinking of the mermaid stories he told her when she was little. Then Sapphy meets a new friend, Faro, who shows her Ingo, a magical underwater world where the Mer live.

As Sapphy spends more time below the waves, she becomes convinced she will find her father in Ingo, but will she have to give up the Air world for good?