SPOILER ALERT! If you haven't read the first two books in the series, Of Poseidon and Of Triton, Stop! I don't want to ruin the series for you.
While traveling, the two of them stop by the side of the highway. The situation heats quickly but is extinguished when someone knocks on the window to see if they need help. Pulling themselves together and not wanting to break any Syrena rules, Galen suggests that they stop since he doesn't want to drive in any bad weather. Emma looks online and sees that there are some caves and springs nearby. They decide to explore one.
Upon finding a spring, the two of them go swimming. Galen finds it odd that no birds are feeding on the school of minnows just below the Warner's surface. He assures Emma that they will be safe from the lightening underwater. Below, they find the entrance to a cave. No fish are around and. Galen wants Emma to stay behind him but eventually they go in side by side. Galen notices that the water feels different to him. Emma kisses his concern away but then he feels it. The pulse in the water isn't lightning strikes nor is it Syrena. Emma finally notices what he is talking about. Galen has a look of panic on his face and realizes that something is ahead of them. A school of fish swims out and Emma tries to question them. She notices that Galen is still staring in front of them. Then, Emma sees a boy swimming without any gear or equipment. He comments that she has the gift of Poseidon and introduces himself as Reed.
Emma quickly realizes the Reed is also a half breed like her. She asks him where he came from and he tells her Neptune. It turns out that Neptune is home not only to half breeds but full Syrena and human who keep their secret. Since half breeds are illegal, Emma wonders how they have evaded detection for so long. With Reed unable to keep his attraction to Emma a secret, Galen becomes possessive. They take Reed back to Neptune and discover that it looks and functions like any other small town except for the mermaid connection. The only "human" in town is a botanist, Mr. Kennedy, who for the past month has been looking for new plant specimens. Against Galen's better judgment, the two check into the B&B to learn about Neptune.
Why did Antonis want Emma to go to Neptune? What do they discover there? Is Mr. Kennedy really a botanist? How has the community gone undetected for so long? Will Emma and Galen be able to weather this latest complication to their relationship?