Diana, a stubborn mermaid, decides to bring a lawsuit to trial against the killers of her mermaid father. Having never lived outside of water before, she gets help from her two sisters (who already live on land) to hunt down the killer. Diana discovers that her sister Venus, one working as an aquatic dancer in a rundown bar, has had her magical crown taken away by the evil barkeep, thus gaining complete control over her. Another sister, named Joan, works at the local aquarium and is able to get the help of her boyfriend, who works as a coastal security commander, to track down their father's killer. The sisters gather their strength and along the way discover how difficult it is to be a fish outside of the water and what a meaningful sisterhood it is.