Charlotte is determined to find out whether or not her grandmother was truly a mermaid, and follows Lewis to Max when he goes to give the research back. Max is delighted to meet the granddaughter of his beloved Gracie, and, not realising that Charlotte is a threat to Emma, Rikki and Cleo, tells her everything. With the girls unaware that Charlotte now knows about them, and also preoccupied with the arrival of the full moon, they are unable to stop her from travelling back to Mako Island and diving into the moon pool just as the full moon passes. The next day, she tells Lewis that she has become a mermaid.