Aria discovers what it's like to have a real mermaid tail, but the deep-sea cities are not the fairytale wonders she dreamed of and she quickly finds herself falling deeper into their problems while still trying to manage her life on land. Torn between worlds, Aria tries to figure out what it is she truly desires.

Becky and Annie were two ordinary teenage girls during World War II. They had dreams of their own, but were content with their peaceful lives. However, everything changed when the circus came to town. Before they knew it, they were on the circus train, their lives being drawn in a whole new direction.

Aria is a professional mermaid at an aquarium. She wears a fake tail and performs for visitors. All her life, she has been in love with the mythical creatures, but her whole world is turned upside down when they turn out to be more than myths and she gets caught in the middle of feuding cities from deep under the sea.

With their city lost and the darkness growing ever stronger, the people of Mirra begin to fear that they may be fighting a losing battle. The guardians refuse to give up, but can they take back the city and restore the power to the lights? In the end, it may be up to the dark prince to decide the fate of Mirra, but they must first find out what he wants from the lights in return. In this final book, light will face off against darkness and the victor will be decided by some children who are out of their world and out of their depth.

The group decided to help Mirra, but they have no idea what that means. As they are trying to figure it out, they meet Azazel, a servant to the shadow master with ties to the royal family. After he put the city in jeopardy, the group must travel to retrieve a stone that could set things right, but do they know the shadow master's true intentions?