India Finch, a part-human / part-mermaid teenager, normally only journeys underwater when she's called upon for her healing abilities. But bored and missing her mer friends, she decides to visit them without being summoned. She soon discovers that without a crisis, life underwater can be just as boring as life on land. To entertain themselves, the mermaids decide to combine all their powers together. This rush of energy creates an enormous tidal wave that threatens human life and puts the merfolk at risk when one of them is photographed. Can India keep the mer from being discovered?