The shy 16-year-old Ruby Gilman (voiced by Lana Condo) wants to integrate into the life of Coast High School, but she always feels that other students turn a blind eye to her as invisible. She is tutoring math for the skateboarding teenager she has a crush on (Yabucci Young-White), but he just seems to admire her good schoolwork, and her eager tiger mother (Toni Klaette) forbids her from going to the beach with her cool classmates at school. She is even strictly forbidden to swim in the water. But when she violates her mother's number one taboo, Ruby finds herself a direct descendant of the siren queen warrior and is destined to inherit her domineering grandmother (voiced by Jane Fonda), the throne of the warrior queen of the seven seas. The siren have vowed to defend the world and all the oceans, and have been fighting vain, power-hungry mermaids from ancient times to the present. But Ruby has a serious and pressing problem: Chelsea (voiced by Anne Murphy), the new transfer student from the school, is not only beautiful and popular, but also happens to be a mermaid. If Ruby wants to protect the person she loves most, she must bravely accept her true identity.