Diana is a mermaid daughter of the moon who, on coming of age, decides to go to the surface to live like humans do. At her university campus she meets Edlyn, Mako, Isla and Lucas, other beings like her. Under the waters of Diana's lagoon she had always been alone, but now she has great friends with whom she shares her day-to-day life. Besides, there's Eiden, that nice human whom she wants to know more about... However, her friendship with him could endanger the lives of all the mermaids and tritons on the planet. Meanwhile, strange things are happening on campus. Students are constantly disappearing, and Isla suspects that the merrows are behind it - another species of mermaid capable of snatching the souls of humans. But the merrows respect the peace pact that was established long ago, so why should they break it now?